Turning Ocean Mixing Upside Down

NASA Astrophysics Data System (ADS)

Ferrari, Raffaele; Mashayek, Ali; Campin, Jean-Michael; McDougall, Trevor; Nikurashin, Maxim

2015-11-01

It is generally understood that small-scale mixing, such as is caused by breaking internal waves, drives upwelling of the densest ocean waters that sink to the ocean bottom at high latitudes. However the observational evidence that small-scale mixing is more vigorous close to the ocean bottom than above implies that small-scale mixing converts light waters into denser ones, thus driving a net sinking of abyssal water. It is shown that abyssal waters return to the surface along weakly stratified boundary layers, where the small-scale mixing of density decays to zero. The net ocean meridional overturning circulation is thus the small residual of a large sinking of waters, driven by small-scale mixing in the stratified interior, and an equally large upwelling, driven by the reduced small-scale mixing along the ocean boundaries. Thus whether abyssal waters upwell or sink in the net cannot be inferred simply from the vertical profile of mixing intensity, but depends also on the ocean hypsometry, i.e. the shape of the bottom topography. The implications of this result for our understanding of the abyssal ocean circulation will be presented with a combination of numerical models and observations.

Antarctic warming driven by internal Southern Ocean deep convection oscillations

NASA Astrophysics Data System (ADS)

Martin, Torge; Pedro, Joel B.; Steig, Eric J.; Jochum, Markus; Park, Wonsun; Rasmussen, Sune O.

2016-04-01

Simulations with the free-running, complex coupled Kiel Climate Model (KCM) show that heat release associated with recurring Southern Ocean deep convection can drive centennial-scale Antarctic temperature variations of 0.5-2.0 °C. We propose a mechanism connecting the intrinsic ocean variability with Antarctic warming that involves the following three steps: Preconditioning: heat supplied by the lower branch of the Atlantic Meridional Overturning Circulation (AMOC) accumulates at depth in the Southern Ocean, trapped by the Weddell Gyre circulation; Convection onset: wind and/or sea-ice changes tip the preconditioned, thermally unstable system into the convective state; Antarctic warming: fast sea-ice-albedo feedbacks (on annual to decadal timescales) and slower Southern Ocean frontal and sea-surface temperature adjustments to the convective heat release (on multi-decadal to centennial timescales), drive an increase in atmospheric heat and moisture transport towards Antarctica resulting in warming over the continent. Further, we discuss the potential role of this mechanism to explain climate variability observed in Antarctic ice-core records.

Transport driven by eddy momentum fluxes in the Gulf Stream Extension region

NASA Astrophysics Data System (ADS)

Greatbatch, R. J.; Zhai, X.; Claus, M.; Czeschel, L.; Rath, W.

2010-12-01

The importance of the Gulf Stream Extension region in climate and seasonal prediction research is being increasingly recognised. Here we use satellite-derived eddy momentum fluxes to drive a shallow water model for the North Atlantic Ocean that includes the realistic ocean bottom topography. The results show that the eddy momentum fluxes can drive significant transport, sufficient to explain the observed increase in transport of the Gulf Stream following its separation from the coast at Cape Hatteras, as well as the observed recirculation gyres. The model also captures recirculating gyres seen in the mean sea surface height field within the North Atlantic Current system east of the Grand Banks of Newfoundland, including a representation of the Mann Eddy.

Biogeochemical modelling of dissolved oxygen in a changing ocean.

PubMed

Andrews, Oliver; Buitenhuis, Erik; Le Quéré, Corinne; Suntharalingam, Parvadha

2017-09-13

Secular decreases in dissolved oxygen concentration have been observed within the tropical oxygen minimum zones (OMZs) and at mid- to high latitudes over the last approximately 50 years. Earth system model projections indicate that a reduction in the oxygen inventory of the global ocean, termed ocean deoxygenation, is a likely consequence of on-going anthropogenic warming. Current models are, however, unable to consistently reproduce the observed trends and variability of recent decades, particularly within the established tropical OMZs. Here, we conduct a series of targeted hindcast model simulations using a state-of-the-art global ocean biogeochemistry model in order to explore and review biases in model distributions of oceanic oxygen. We show that the largest magnitude of uncertainty is entrained into ocean oxygen response patterns due to model parametrization of p CO 2 -sensitive C : N ratios in carbon fixation and imposed atmospheric forcing data. Inclusion of a p CO 2 -sensitive C : N ratio drives historical oxygen depletion within the ocean interior due to increased organic carbon export and subsequent remineralization. Atmospheric forcing is shown to influence simulated interannual variability in ocean oxygen, particularly due to differences in imposed variability of wind stress and heat fluxes.This article is part of the themed issue 'Ocean ventilation and deoxygenation in a warming world'. © 2017 The Author(s).

Biogeochemical modelling of dissolved oxygen in a changing ocean

NASA Astrophysics Data System (ADS)

Andrews, Oliver; Buitenhuis, Erik; Le Quéré, Corinne; Suntharalingam, Parvadha

2017-08-01

Secular decreases in dissolved oxygen concentration have been observed within the tropical oxygen minimum zones (OMZs) and at mid- to high latitudes over the last approximately 50 years. Earth system model projections indicate that a reduction in the oxygen inventory of the global ocean, termed ocean deoxygenation, is a likely consequence of on-going anthropogenic warming. Current models are, however, unable to consistently reproduce the observed trends and variability of recent decades, particularly within the established tropical OMZs. Here, we conduct a series of targeted hindcast model simulations using a state-of-the-art global ocean biogeochemistry model in order to explore and review biases in model distributions of oceanic oxygen. We show that the largest magnitude of uncertainty is entrained into ocean oxygen response patterns due to model parametrization of pCO2-sensitive C : N ratios in carbon fixation and imposed atmospheric forcing data. Inclusion of a pCO2-sensitive C : N ratio drives historical oxygen depletion within the ocean interior due to increased organic carbon export and subsequent remineralization. Atmospheric forcing is shown to influence simulated interannual variability in ocean oxygen, particularly due to differences in imposed variability of wind stress and heat fluxes. This article is part of the themed issue 'Ocean ventilation and deoxygenation in a warming world'.

Determining the Ocean's Role on the Variable Gravity Field on Earth Rotation

NASA Technical Reports Server (NTRS)

Ponte, Rui M.

1999-01-01

A number of ocean models of different complexity have been used to study changes in the oceanic mass field and angular momentum and their relation to the variable Earth rotation and gravity field. Time scales examined range from seasonal to a few days. Results point to the importance of oceanic signals in driving polar motion, in particular the Chandler and annual wobbles. Results also show that oceanic signals have a measurable impact on length-of-day variations. Various circulation features and associated mass signals, including the North Pacific subtropical gyre, the equatorial currents, and the Antarctic Circumpolar Current play a significant role in oceanic angular momentum variability.

Global decadal climate variability driven by Southern Ocean convection

NASA Astrophysics Data System (ADS)

Marinov, I.; Cabre, A.

2016-02-01

Here we suggest a set of new "teleconnections" by which the Southern Ocean (SO) can induce anomalies in the tropical oceans and atmosphere. A 5000-year long control simulation in a coupled atmosphere-ocean model (CM2Mc, a low-resolution GFDL model) shows a natural, highly regular multi-decadal oscillation between periods of SO open sea convection and non-convective periods. This process happens naturally, with different frequencies and durations of convection across the majority of CMIP5 under preindustrial forcing (deLavergne et al., 2014). In our model, oscillations in Weddell Sea convection drive multidecadal variability in SO and global SSTs, as well as SO heat storage, with convective decades warm due to the heat released from the Circumpolar Deep Water and non-convective decades cold due to subsurface heat storage. Convective pulses drive local SST and sea ice variations south of 60S, immediately triggering changes in the Ferrell and Hadley cells, atmospheric energy budget and cross-equatorial heat exchange, ultimately influencing the position of the Intertropical Convergence Zone and rain patterns in the tropics. Additionally, the SO convection pulse is propagated to the tropics and the North Atlantic MOC via oceanic pathways on relatively fast (decadal) timescales, in agreement with recent observational constraints. Open sea convection is the major mode of Antarctic Bottom Water (AABW) formation in the CMIP5 models. Future improvements in the representation of shelf convection and sea-ice interaction in the SO are a clear necessity. These model improvements should render the AABW representation more realistic, and might influence (a) the connectivity of the SO with the rest of the planet, as described above and (b) the oceanic and global carbon cycle, of which the AABW is a fundamental conduit.

The use of stellite scatterometer winds to drive a primitive equation model of the Indian Ocean: The impact of bandlike sampling

NASA Technical Reports Server (NTRS)

Barnier, Bernard; Capella, Jorge; O'Brien, James J.

1994-01-01

The aim of this study is to evaluate the impact of the bandlike sampling of spaceborne scatterometers on the ability of scatterometer winds to successfully force the mean flow and seasonal cycle of an ocean model in the context of equatorial and tropical dynamics. The equatorial ocean is simulated with a four-layer, primitive equation, reduced gravity model of the Indian Ocean. The variable wind stress used in this study is derived from one year (1988) of 6-hour analyses of the 10-m wind vector over the Indian Ocean performed at the European Centre for Medium-Range Weather Forecasts (ECMWF). It is applied as a forcing at every grid point of the model to drive a reference circulation. Scatterometer winds are simulated from ECMWF winds, using the nominal configurations and orbital parameters of the European Remote Sensing 1 (ERS-1) and NASA Scatterometer (NSCAT) missions. The model is forced in real time under swaths with the raw scatterometer winds of ERS-1 and NSCAT, with a persistence condition (i.e., the wind is kept constsnt until the next passage of the satellite provides a new value). The circulation obtained for each of the scatterometer experiments is compared with the reference circulation. The seasonal circulation of the Indian Ocean with NSCAT winds is very similar to the reference. The perturbations introduced by the bandlike sampling and the persistance condition have an impact similar to that of a small uncorrelated noise added to the reference forcing. The persistence condition for ERS-1 does not give results which are as good as those obtained for NSCAT.

Factors driving mercury variability in the Arctic atmosphere and ocean over the past 30 years

NASA Astrophysics Data System (ADS)

Fisher, Jenny A.; Jacob, Daniel J.; Soerensen, Anne L.; Amos, Helen M.; Corbitt, Elizabeth S.; Streets, David G.; Wang, Qiaoqiao; Yantosca, Robert M.; Sunderland, Elsie M.

2013-12-01

observations at Arctic sites (Alert and Zeppelin) show large interannual variability (IAV) in atmospheric mercury (Hg), implying a strong sensitivity of Hg to environmental factors and potentially to climate change. We use the GEOS-Chem global biogeochemical Hg model to interpret these observations and identify the principal drivers of spring and summer IAV in the Arctic atmosphere and surface ocean from 1979-2008. The model has moderate skill in simulating the observed atmospheric IAV at the two sites (r 0.4) and successfully reproduces a long-term shift at Alert in the timing of the spring minimum from May to April (r = 0.7). Principal component analysis indicates that much of the IAV in the model can be explained by a single climate mode with high temperatures, low sea ice fraction, low cloudiness, and shallow boundary layer. This mode drives decreased bromine-driven deposition in spring and increased ocean evasion in summer. In the Arctic surface ocean, we find that the IAV for modeled total Hg is dominated by the meltwater flux of Hg previously deposited to sea ice, which is largest in years with high solar radiation (clear skies) and cold spring air temperature. Climate change in the Arctic is projected to result in increased cloudiness and strong warming in spring, which may thus lead to decreased Hg inputs to the Arctic Ocean. The effect of climate change on Hg discharges from Arctic rivers remains a major source of uncertainty.

Efficient Flowline Simulations of Ice Shelf-Ocean Interactions: Sensitivity Studies with a Fully Coupled Model

NASA Technical Reports Server (NTRS)

Walker, Ryan Thomas; Holland, David; Parizek, Byron R.; Alley, Richard B.; Nowicki, Sophie M. J.; Jenkins, Adrian

2013-01-01

Thermodynamic flowline and plume models for the ice shelf-ocean system simplify the ice and ocean dynamics sufficiently to allow extensive exploration of parameters affecting ice-sheet stability while including key physical processes. Comparison between geophysically and laboratory-based treatments of ice-ocean interface thermodynamics shows reasonable agreement between calculated melt rates, except where steep basal slopes and relatively high ocean temperatures are present. Results are especially sensitive to the poorly known drag coefficient, highlighting the need for additional field experiments to constrain its value. These experiments also suggest that if the ice-ocean interface near the grounding line is steeper than some threshold, further steepening of the slope may drive higher entrainment that limits buoyancy, slowing the plume and reducing melting; if confirmed, this will provide a stabilizing feedback on ice sheets under some circumstances.

Regional model simulation of summer rainfall over the Philippines: Effect of choice of driving fields and ocean flux schemes

NASA Astrophysics Data System (ADS)

Francisco, R. V.; Argete, J.; Giorgi, F.; Pal, J.; Bi, X.; Gutowski, W. J.

2006-09-01

The latest version of the Abdus Salam International Centre for Theoretical Physics (ICTP) regional model RegCM is used to investigate summer monsoon precipitation over the Philippine archipelago and surrounding ocean waters, a region where regional climate models have not been applied before. The sensitivity of simulated precipitation to driving lateral boundary conditions (NCEP and ERA40 reanalyses) and ocean surface flux scheme (BATS and Zeng) is assessed for 5 monsoon seasons. The ability of the RegCM to simulate the spatial patterns and magnitude of monsoon precipitation is demonstrated, both in response to the prominent large scale circulations over the region and to the local forcing by the physiographical features of the Philippine islands. This provides encouraging indications concerning the development of a regional climate modeling system for the Philippine region. On the other hand, the model shows a substantial sensitivity to the analysis fields used for lateral boundary conditions as well as the ocean surface flux schemes. The use of ERA40 lateral boundary fields consistently yields greater precipitation amounts compared to the use of NCEP fields. Similarly, the BATS scheme consistently produces more precipitation compared to the Zeng scheme. As a result, different combinations of lateral boundary fields and surface ocean flux schemes provide a good simulation of precipitation amounts and spatial structure over the region. The response of simulated precipitation to using different forcing analysis fields is of the same order of magnitude as the response to using different surface flux parameterizations in the model. As a result it is difficult to unambiguously establish which of the model configurations is best performing.

Deep winter convection and phytoplankton dynamics in the NW Mediterranean Sea under present climate and future (horizon 2030) scenarios.

PubMed

Macias, Diego; Garcia-Gorriz, Elisa; Stips, Adolf

2018-04-26

Deep water convection (DC) in winter is one of the major processes driving open-ocean primary productivity in the Northwestern Mediterranean Sea. DC is highly variable in time, depending on the specific conditions (stratification, circulation and ocean-atmosphere interactions) of each specific winter. This variability also drives the interannual oscillations of open-ocean primary productivity in this important region for many commercially-important fish species. We use a coupled model system to 1) understand to what extent DC impacts phytoplankton seasonality in the present-day and 2) to explore potential changes in future scenarios (~2030). Our model represents quite accurately the present-day characteristics of DC and its importance for open-ocean phytoplankton blooms. However, for the future scenarios the importance of deep nutrients in fertilizing the euphotic layer of the NW Mediterranean decreases. The model simulates changes in surface density and on the levels of kinetic energy that make mesoscale activity associated with horizontal currents to become a more important fertilization mechanism, inducing subsequently phenological changes in seasonal plankton cycles. Because of our focus on the open-sea, an exact quantification of the impact of those changes on the overall biological production of the NW Mediterranean cannot be made at the moment.

Impacts of the IOD-associated temperature and salinity anomalies on the intermittent equatorial undercurrent anomalies

NASA Astrophysics Data System (ADS)

Li, Junde; Liang, Chujin; Tang, Youmin; Liu, Xiaohui; Lian, Tao; Shen, Zheqi; Li, Xiaojing

2017-11-01

The study of Equatorial Undercurrent (EUC) has attracted a broad attention in recent years due to its strong response and feedback to the Indian Ocean Dipole. In this paper, we first produce a high-quality simulation of three-dimensional temperature, salinity and zonal current simulation from 1982 to 2014, using a high-resolution ocean general circulation model. On this basis, with two sensitivity experiments, we investigate the role of temperature and salinity anomalies in driving and enhancing the EUC during the positive IOD events by examining the variation of the EUC seasonal cycle and diagnosing the zonal momentum budget along the equatorial Indian Ocean. Our results show that during January-March, the EUC can appear along the entire equatorial Indian Ocean in all years, but during August-November, the EUC can appear and reach the eastern Indian Ocean only during the positive IOD events. The zonal momentum budget analysis indicates that the pressure gradient force contributes most to the variation of the eastward acceleration of zonal currents in the subsurface. During the positive IOD events, strong negative subsurface temperature anomalies exist in the eastern Indian Ocean, with negative surface salinity anomalies in the central and eastern Indian Ocean, resulting in a large pressure gradient force to drive EUC during the August-November. Further, the results of two sensitivity experiments indicate that the temperature anomalies significantly impact the pressure gradient force, playing a leading role in driving the EUC, while the surface salinity anomalies can secondarily help to intensify the eastward EUC through increasing the zonal density gradient in the eastern Indian Ocean and impacting the vertical momentum advection in the subsurface.

Interhemispheric gradient of atmospheric radiocarbon reveals natural variability of Southern Ocean winds

NASA Astrophysics Data System (ADS)

Rodgers, K. B.; Mikaloff-Fletcher, S. E.; Bianchi, D.; Beaulieu, C.; Galbraith, E. D.; Gnanadesikan, A.; Hogg, A. G.; Iudicone, D.; Lintner, B. R.; Naegler, T.; Reimer, P. J.; Sarmiento, J. L.; Slater, R. D.

2011-10-01

Tree ring Δ14C data (Reimer et al., 2004; McCormac et al., 2004) indicate that atmospheric Δ14C varied on multi-decadal to centennial timescales, in both hemispheres, over the period between AD 950 and 1830. The Northern and Southern Hemispheric Δ14C records display similar variability, but from the data alone is it not clear whether these variations are driven by the production of 14C in the stratosphere (Stuiver and Quay, 1980) or by perturbations to exchanges between carbon reservoirs (Siegenthaler et al., 1980). As the sea-air flux of 14CO2 has a clear maximum in the open ocean regions of the Southern Ocean, relatively modest perturbations to the winds over this region drive significant perturbations to the interhemispheric gradient. In this study, model simulations are used to show that Southern Ocean winds are likely a main driver of the observed variability in the interhemispheric gradient over AD 950-1830, and further, that this variability may be larger than the Southern Ocean wind trends that have been reported for recent decades (notably 1980-2004). This interpretation also implies that there may have been a significant weakening of the winds over the Southern Ocean within a few decades of AD 1375, associated with the transition between the Medieval Climate Anomaly and the Little Ice Age. The driving forces that could have produced such a shift in the winds at the Medieval Climate Anomaly to Little Ice Age transition remain unknown. Our process-focused suite of perturbation experiments with models raises the possibility that the current generation of coupled climate and earth system models may underestimate the natural background multi-decadal- to centennial-timescale variations in the winds over the Southern Ocean.

Multimillennium changes in dissolved oxygen under global warming: results from an AOGCM and offline ocean biogeochemical model

NASA Astrophysics Data System (ADS)

Yamamoto, A.; Abe-Ouchi, A.; Shigemitsu, M.; Oka, A.; Takahashi, K.; Ohgaito, R.; Yamanaka, Y.

2016-12-01

Long-term oceanic oxygen change due to global warming is still unclear; most future projections (such as CMIP5) are only performed until 2100. Indeed, few previous studies using conceptual models project oxygen change in the next thousands of years, showing persistent global oxygen reduction by about 30% in the next 2000 years, even after atmospheric carbon dioxide stops rising. Yet, these models cannot sufficiently represent the ocean circulation change: the key driver of oxygen change. Moreover, considering serious effect oxygen reduction has on marine life and biogeochemical cycling, long-term oxygen change should be projected for higher validity. Therefore, we used a coupled atmosphere-ocean general circulation model (AOGCM) and an offline ocean biogeochemical model, investigating realistic long-term changes in oceanic oxygen concentration and ocean circulation. We integrated these models for 2000 years under atmospheric CO2 doubling and quadrupling. After global oxygen reduction in the first 500 years, oxygen concentration in deep ocean globally recovers and overshoots, despite surface oxygen decrease and weaker Atlantic Meridional Overturning Circulation. Deep ocean convection in the Weddell Sea recovers and overshoots, after initial cessation. Thus, enhanced deep convection and associated Antarctic Bottom Water supply oxygen-rich surface waters to deep ocean, resulting global deep ocean oxygenation. We conclude that the change in ocean circulation in the Southern Ocean potentially drives millennial-scale oxygenation in the deep ocean; contrary to past reported long-term oxygen reduction and general expectation. In presentation, we will discuss the mechanism of response of deep ocean convection in the Weddell Sea and show the volume changes of hypoxic waters.

Investigation of land ice-ocean interaction with a fully coupled ice-ocean model: 1. Model description and behavior

NASA Astrophysics Data System (ADS)

Goldberg, D. N.; Little, C. M.; Sergienko, O. V.; Gnanadesikan, A.; Hallberg, R.; Oppenheimer, M.

2012-06-01

Antarctic ice shelves interact closely with the ocean cavities beneath them, with ice shelf geometry influencing ocean cavity circulation, and heat from the ocean driving changes in the ice shelves, as well as the grounded ice streams that feed them. We present a new coupled model of an ice stream-ice shelf-ocean system that is used to study this interaction. The model is capable of representing a moving grounding line and dynamically responding ocean circulation within the ice shelf cavity. Idealized experiments designed to investigate the response of the coupled system to instantaneous increases in ocean temperature show ice-ocean system responses on multiple timescales. Melt rates and ice shelf basal slopes near the grounding line adjust in 1-2 years, and downstream advection of the resulting ice shelf thinning takes place on decadal timescales. Retreat of the grounding line and adjustment of grounded ice takes place on a much longer timescale, and the system takes several centuries to reach a new steady state. During this slow retreat, and in the absence of either an upward-or downward-sloping bed or long-term trends in ocean heat content, the ice shelf and melt rates maintain a characteristic pattern relative to the grounding line.

Oceanic crustal carbon cycle drives 26-million-year atmospheric carbon dioxide periodicities.

PubMed

Müller, R Dietmar; Dutkiewicz, Adriana

2018-02-01

Atmospheric carbon dioxide (CO 2 ) data for the last 420 million years (My) show long-term fluctuations related to supercontinent cycles as well as shorter cycles at 26 to 32 My whose origin is unknown. Periodicities of 26 to 30 My occur in diverse geological phenomena including mass extinctions, flood basalt volcanism, ocean anoxic events, deposition of massive evaporites, sequence boundaries, and orogenic events and have previously been linked to an extraterrestrial mechanism. The vast oceanic crustal carbon reservoir is an alternative potential driving force of climate fluctuations at these time scales, with hydrothermal crustal carbon uptake occurring mostly in young crust with a strong dependence on ocean bottom water temperature. We combine a global plate model and oceanic paleo-age grids with estimates of paleo-ocean bottom water temperatures to track the evolution of the oceanic crustal carbon reservoir over the past 230 My. We show that seafloor spreading rates as well as the storage, subduction, and emission of oceanic crustal and mantle CO 2 fluctuate with a period of 26 My. A connection with seafloor spreading rates and equivalent cycles in subduction zone rollback suggests that these periodicities are driven by the dynamics of subduction zone migration. The oceanic crust-mantle carbon cycle is thus a previously overlooked mechanism that connects plate tectonic pulsing with fluctuations in atmospheric carbon and surface environments.

Oceanic crustal carbon cycle drives 26-million-year atmospheric carbon dioxide periodicities

PubMed Central

Müller, R. Dietmar; Dutkiewicz, Adriana

2018-01-01

Atmospheric carbon dioxide (CO2) data for the last 420 million years (My) show long-term fluctuations related to supercontinent cycles as well as shorter cycles at 26 to 32 My whose origin is unknown. Periodicities of 26 to 30 My occur in diverse geological phenomena including mass extinctions, flood basalt volcanism, ocean anoxic events, deposition of massive evaporites, sequence boundaries, and orogenic events and have previously been linked to an extraterrestrial mechanism. The vast oceanic crustal carbon reservoir is an alternative potential driving force of climate fluctuations at these time scales, with hydrothermal crustal carbon uptake occurring mostly in young crust with a strong dependence on ocean bottom water temperature. We combine a global plate model and oceanic paleo-age grids with estimates of paleo-ocean bottom water temperatures to track the evolution of the oceanic crustal carbon reservoir over the past 230 My. We show that seafloor spreading rates as well as the storage, subduction, and emission of oceanic crustal and mantle CO2 fluctuate with a period of 26 My. A connection with seafloor spreading rates and equivalent cycles in subduction zone rollback suggests that these periodicities are driven by the dynamics of subduction zone migration. The oceanic crust-mantle carbon cycle is thus a previously overlooked mechanism that connects plate tectonic pulsing with fluctuations in atmospheric carbon and surface environments. PMID:29457135

A Comparison Study and Software Implementation of NORDA Ocean Models.

DTIC Science & Technology

1980-10-08

L01?C07 ’EEEEElshhhh A COMPARISON STUDY AND SOFTWARE IMPLEMENTATION OF NORDA OCEAN MODELS J&IEA m/ MST* f-....~ cre mx IRSD~I?( J 300 Unicorn Park...34- NOO-79- 741 9. PERFORMING ORGANIZATION NAME AND ADDRESS 10. PROGRAM ELEMENT. PROJECT, TASK AREA 6 WORK UNIT NUMBERSJAYC0, 300 Unicorn Park Drive...before another execution of the energetics program, move them back to disk. Note that the outputs of the preprocessor reside on disk, they should not be

Near-inertial Wave Studies using Historical Mooring Records and a High-Resolution General Circulation Model

DTIC Science & Technology

2009-01-01

Mooring Records and a High- Resolution General Circulation Model Harper Simmons School of Fisheries and Ocean Sciences 903 Koyukuk Drive Fairbanks AK...oceanographic community has been to develop a global internal wave prediction system analogous to those already in place for surface waves. Early steps have...AUTHOR(S) 5d. PROJECT NUMBER 5e. TASK NUMBER 5f. WORK UNIT NUMBER 7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES) School of Fisheries and Ocean

Hydrothermal systems in small ocean planets.

PubMed

Vance, Steve; Harnmeijer, Jelte; Kimura, Jun; Hussmann, Hauke; Demartin, Brian; Brown, J Michael

2007-12-01

We examine means for driving hydrothermal activity in extraterrestrial oceans on planets and satellites of less than one Earth mass, with implications for sustaining a low level of biological activity over geological timescales. Assuming ocean planets have olivine-dominated lithospheres, a model for cooling-induced thermal cracking shows how variation in planet size and internal thermal energy may drive variation in the dominant type of hydrothermal system-for example, high or low temperature system or chemically driven system. As radiogenic heating diminishes over time, progressive exposure of new rock continues to the current epoch. Where fluid-rock interactions propagate slowly into a deep brittle layer, thermal energy from serpentinization may be the primary cause of hydrothermal activity in small ocean planets. We show that the time-varying hydrostatic head of a tidally forced ice shell may drive hydrothermal fluid flow through the seafloor, which can generate moderate but potentially important heat through viscous interaction with the matrix of porous seafloor rock. Considering all presently known potential ocean planets-Mars, a number of icy satellites, Pluto, and other trans-neptunian objects-and applying Earth-like material properties and cooling rates, we find depths of circulation are more than an order of magnitude greater than in Earth. In Europa and Enceladus, tidal flexing may drive hydrothermal circulation and, in Europa, may generate heat on the same order as present-day radiogenic heat flux at Earth's surface. In all objects, progressive serpentinization generates heat on a globally averaged basis at a fraction of a percent of present-day radiogenic heating and hydrogen is produced at rates between 10(9) and 10(10) molecules cm(2) s(1).

Processes driving sea ice variability in the Bering Sea in an eddying ocean/sea ice model: Mean seasonal cycle

NASA Astrophysics Data System (ADS)

Li, Linghan; McClean, Julie L.; Miller, Arthur J.; Eisenman, Ian; Hendershott, Myrl C.; Papadopoulos, Caroline A.

2014-12-01

The seasonal cycle of sea ice variability in the Bering Sea, together with the thermodynamic and dynamic processes that control it, are examined in a fine resolution (1/10°) global coupled ocean/sea-ice model configured in the Community Earth System Model (CESM) framework. The ocean/sea-ice model consists of the Los Alamos National Laboratory Parallel Ocean Program (POP) and the Los Alamos Sea Ice Model (CICE). The model was forced with time-varying reanalysis atmospheric forcing for the time period 1970-1989. This study focuses on the time period 1980-1989. The simulated seasonal-mean fields of sea ice concentration strongly resemble satellite-derived observations, as quantified by root-mean-square errors and pattern correlation coefficients. The sea ice energy budget reveals that the seasonal thermodynamic ice volume changes are dominated by the surface energy flux between the atmosphere and the ice in the northern region and by heat flux from the ocean to the ice along the southern ice edge, especially on the western side. The sea ice force balance analysis shows that sea ice motion is largely associated with wind stress. The force due to divergence of the internal ice stress tensor is large near the land boundaries in the north, and it is small in the central and southern ice-covered region. During winter, which dominates the annual mean, it is found that the simulated sea ice was mainly formed in the northern Bering Sea, with the maximum ice growth rate occurring along the coast due to cold air from northerly winds and ice motion away from the coast. South of St Lawrence Island, winds drive the model sea ice southwestward from the north to the southwestern part of the ice-covered region. Along the ice edge in the western Bering Sea, model sea ice is melted by warm ocean water, which is carried by the simulated Bering Slope Current flowing to the northwest, resulting in the S-shaped asymmetric ice edge. In spring and fall, similar thermodynamic and dynamic patterns occur in the model, but with typically smaller magnitudes and with season-specific geographical and directional differences.

The relationship between cadmium and phosphate in the Atlantic Ocean unravelled

NASA Astrophysics Data System (ADS)

Middag, Rob; van Heuven, Steven M. A. C.; Bruland, Kenneth W.; de Baar, Hein J. W.

2018-06-01

Cadmium (Cd) is not generally considered a nutrient element, but behaves like a nutrient in the oceans and might play an important role in ocean biology after all. The relationship between Cd and the nutrient phosphate (PO4) has been studied for over 40 yrs, but the debate on the driving mechanism and reason behind the 'kink', a change in the steepness of the slope is ongoing. Using new data of high accuracy and spatial resolution covering the West-Atlantic Ocean from north to south, in combination with a robust extended optimum multiparameter (eOMP) water mass model, we show that mixing between different water masses is the dominant factor explaining the observed correlation and its kink. Regeneration of Cd via remineralisation explains the smaller scale variability, notably in the surface ocean. Observations imply the availability of Cd in surface waters determines the Cd-uptake and thus the Cd:PO4 remineralisation ratio. This ratio is variable between different ocean regions, notably between the northern and southern high latitude oceans. Due to their role in deep water formation, both the northern and southern high latitude oceans are a driving factor in the Atlantic and global Cd and PO4 relation. Outside the Atlantic Ocean, the classical kink is not expected, but the relationship is by no means linear. Most likely, this is due to the interaction between low latitude surface waters and subsurface waters from high latitude origin, but more data are required to assess this in detail.

Can the Ocean's Heat Engine Control Horizontal Circulation? Insights From the Caspian Sea

NASA Astrophysics Data System (ADS)

Bruneau, Nicolas; Zika, Jan; Toumi, Ralf

2017-10-01

We investigate the role of the ocean's heat engine in setting horizontal circulation using a numerical model of the Caspian Sea. The Caspian Sea can be seen as a virtual laboratory—a compromise between realistic global models that are hampered by long equilibration times and idealized basin geometry models, which are not constrained by observations. We find that increases in vertical mixing drive stronger thermally direct overturning and consequent conversion of available potential to kinetic energy. Numerical solutions with water mass structures closest to observations overturn 0.02-0.04 × 106 m3/s (sverdrup) representing the first estimate of Caspian Sea overturning. Our results also suggest that the overturning is thermally forced increasing in intensity with increasing vertical diffusivity. Finally, stronger thermally direct overturning is associated with a stronger horizontal circulation in the Caspian Sea. This suggests that the ocean's heat engine can strongly impact broader horizontal circulations in the ocean.

Determining the Ocean's Role on the Variable Gravity Field and Earth Rotation

NASA Technical Reports Server (NTRS)

Ponte, Rui M.; Frey, H. (Technical Monitor)

2000-01-01

A number of ocean models of different complexity have been used to study changes in the oceanic angular momentum (OAM) and mass fields and their relation to the variable Earth rotation and gravity field. Time scales examined range from seasonal to a few days. Results point to the importance of oceanic signals in driving polar motion, in particular the Chandler and annual wobbles. Results also show that oceanic signals have a measurable impact on length-of-day variations. Various circulation features and associated mass signals, including the North Pacific subtropical gyre, the equatorial currents, and the Antarctic Circumpolar Current play a significant role in oceanic angular momentum variability. The impact on OAM values of an optimization procedure that uses available data to constrain ocean model results was also tested for the first time. The optimization procedure yielded substantial changes, in OAM, related to adjustments in both motion and mass fields,as well as in the wind stress torques acting on the ocean. Constrained OAM values were found to yield noticeable improvements in the agreement with the observed Earth rotation parameters, particularly at the seasonal timescale.

Ice-sheet response to oceanic forcing.

PubMed

Joughin, Ian; Alley, Richard B; Holland, David M

2012-11-30

The ice sheets of Greenland and Antarctica are losing ice at accelerating rates, much of which is a response to oceanic forcing, especially of the floating ice shelves. Recent observations establish a clear correspondence between the increased delivery of oceanic heat to the ice-sheet margin and increased ice loss. In Antarctica, most of these processes are reasonably well understood but have not been rigorously quantified. In Greenland, an understanding of the processes by which warmer ocean temperatures drive the observed retreat remains elusive. Experiments designed to identify the relevant processes are confounded by the logistical difficulties of instrumenting ice-choked fjords with actively calving glaciers. For both ice sheets, multiple challenges remain before the fully coupled ice-ocean-atmosphere models needed for rigorous sea-level projection are available.

Results from ISOMIP+ and MISOMIP1, two interrelated marine ice sheet and ocean model intercomparison projects

NASA Astrophysics Data System (ADS)

Asay-Davis, X.; Galton-Fenzi, B.; Gwyther, D.; Jourdain, N.; Martin, D. F.; Nakayama, Y.; Seroussi, H. L.

2016-12-01

MISMIP+ (the third Marine Ice Sheet MIP), ISOMIP+ (the second Ice Shelf-Ocean MIP) and MISOMIP1 (the first Marine Ice Sheet-Ocean MIP) prescribe a set of idealized experiments for marine ice-sheet models, ocean models with ice-shelf cavities, and coupled ice sheet-ocean models, respectively. Here, we present results from ISOMIP+ and MISOMIP1 experiments using several ocean-only and coupled ice sheet-ocean models. Among the ocean models, we show that differences in model behavior are significant enough that similar results can only be achieved by tuning model parameters (the heat- and salt-transfer coefficients across the sub-ice-shelf boundary layer) for each model. This tuning is constrained by a desired mean melt rate in quasi-steady state under specified forcing conditions, akin to tuning the models to match observed melt rates. We compare the evolution of ocean temperature transects, melt rate, friction velocity and thermal driving between ocean models for the five ISOMIP+ experiments (Ocean0-4), which have prescribed ice-shelf topography. We find that melt patterns differ between models based on the relative importance of overturning strength and vertical mixing of temperature even when the models have been tuned to achieve similar melt rates near the grounding line. For the two MISOMIP1 experiments (IceOcean1 without dynamic calving and IceOcean2 with a simple calving parameterization), we compare temperature transects, melt rate, ice-shelf topography and grounded area across models and for several model configurations. Consistent with preliminary results from MISMIP+, we find that for a given coupled model, the use of a Coulomb-limited basal friction parameterization below grounded ice and the application of dynamic calving both significantly increase the rate of grounding-line retreat, whereas the rate of retreat appears to be less sensitive to the ice stress approximation (shallow-shelf approximation, higher-order, etc.). We show that models with similar mean melt rates, stress approximations and basal friction parameterizations produce markedly different rates of grounding-line retreat, and we investigate possible sources of these disparities (e.g. differences in coupling strategy or melt distribution).

Anticipated Improvements to Net Surface Freshwater Fluxes from GPM

NASA Technical Reports Server (NTRS)

Smith, Eric A.

2005-01-01

Evaporation and precipitation over the oceans play very important roles in the global water cycle, upper-ocean heat budget, ocean dynamics, and coupled ocean-atmosphere dynamics. In the conventional representation of the terrestrial water cycle, the assumed role of the oceans is to act as near-infinite reservoirs of water with the main drivers of the water cycle being land- atmosphere interactions in which excess precipitation (P) over evaporation (E) is returned to the oceans as surface runoff and baseflow. Whereas this perspective is valid for short space and time scales -- fundamental principles, available observed estimates, and results from models indicate that the oceans play a far more important role in the large-scale water cycle at seasonal and longer timescales. Approximately 70-80% of the total global evaporation and precipitation occurs over oceans. Moreover, latent heat release into the atmosphere over the oceans is the major heat source driving global atmospheric circulations, with the moisture transported by circulations from oceans to continents being the major source of water precipitating over land. Notably, the major impediment in understanding and modeling the oceans role in the global water cycle is the lack of reliable net surface freshwater flux estimates (E - P fluxes) at the salient spatial and temporal resolutions, i.e., consistent coupled weekly to monthly E - P gridded datasets.

Mesoscale atmosphere ocean coupling enhances the transfer of wind energy into the ocean

PubMed Central

Byrne, D.; Münnich, M.; Frenger, I.; Gruber, N.

2016-01-01

Although it is well established that the large-scale wind drives much of the world's ocean circulation, the contribution of the wind energy input at mesoscales (10–200 km) remains poorly known. Here we use regional simulations with a coupled high-resolution atmosphere–ocean model of the South Atlantic, to show that mesoscale ocean features and, in particular, eddies can be energized by their thermodynamic interactions with the atmosphere. Owing to their sea-surface temperature anomalies affecting the wind field above them, the oceanic eddies in the presence of a large-scale wind gradient provide a mesoscale conduit for the transfer of energy into the ocean. Our simulations show that this pathway is responsible for up to 10% of the kinetic energy of the oceanic mesoscale eddy field in the South Atlantic. The conditions for this pathway to inject energy directly into the mesoscale prevail over much of the Southern Ocean north of the Polar Front. PMID:27292447

The de-correlation of westerly winds and westerly-wind stress over the Southern Ocean during the Last Glacial Maximum

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu, Wei; Lu, Jian; Leung, Lai-Yung R.

2015-02-22

This paper investigates the changes of the Southern Westerly Winds (SWW) and Southern Ocean (SO) upwelling between the Last Glacial Maximum (LGM) and preindustrial (PI) in the PMIP3/CMIP5 simulations, highlighting the role of the Antarctic sea ice in modulating the wind stress effect on the ocean. Particularly, a discrepancy may occur between the changes in SWW and westerly wind stress, caused primarily by an equatorward expansion of winter Antarctic sea ice that undermines the wind stress in driving the liquid ocean. Such discrepancy may reflect the LGM condition in reality, in view of that the model simulates this condition hasmore » most credible simulation of modern SWW and Antarctic sea ice. The effect of wind stress on the SO upwelling is further explored via the wind-induced Ekman pumping, which is reduced under the LGM condition in all models, in part by the sea-ice “capping” effect present in the models.« less

SAR observation and model tracking of an oil spill event in coastal waters.

PubMed

Cheng, Yongcun; Li, Xiaofeng; Xu, Qing; Garcia-Pineda, Oscar; Andersen, Ole Baltazar; Pichel, William G

2011-02-01

Oil spills are a major contributor to marine pollution. The objective of this work is to simulate the oil spill trajectory of oil released from a pipeline leaking in the Gulf of Mexico with the GNOME (General NOAA Operational Modeling Environment) model. The model was developed by NOAA (National Oceanic and Atmospheric Administration) to investigate the effects of different pollutants and environmental conditions on trajectory results. Also, a Texture-Classifying Neural Network Algorithm (TCNNA) was used to delineate ocean oil slicks from synthetic aperture radar (SAR) observations. During the simulation, ocean currents from NCOM (Navy Coastal Ocean Model) outputs and surface wind data measured by an NDBC (National Data Buoy Center) buoy are used to drive the GNOME model. The results show good agreement between the simulated trajectory of the oil spill and synchronous observations from the European ENVISAT ASAR (Advanced Synthetic Aperture Radar) and the Japanese ALOS (Advanced Land Observing Satellite) PALSAR (Phased Array L-band Synthetic Aperture Radar) images. Based on experience with past marine oil spills, about 63.0% of the oil will float and 18.5% of the oil will evaporate and disperse. In addition, the effects from uncertainty of ocean currents and the diffusion coefficient on the trajectory results are also studied. Copyright © 2010 Elsevier Ltd. All rights reserved.

Global assessment of ocean carbon export by combining satellite observations and food-web models

NASA Astrophysics Data System (ADS)

Siegel, D. A.; Buesseler, K. O.; Doney, S. C.; Sailley, S. F.; Behrenfeld, M. J.; Boyd, P. W.

2014-03-01

The export of organic carbon from the surface ocean by sinking particles is an important, yet highly uncertain, component of the global carbon cycle. Here we introduce a mechanistic assessment of the global ocean carbon export using satellite observations, including determinations of net primary production and the slope of the particle size spectrum, to drive a food-web model that estimates the production of sinking zooplankton feces and algal aggregates comprising the sinking particle flux at the base of the euphotic zone. The synthesis of observations and models reveals fundamentally different and ecologically consistent regional-scale patterns in export and export efficiency not found in previous global carbon export assessments. The model reproduces regional-scale particle export field observations and predicts a climatological mean global carbon export from the euphotic zone of 6 Pg C yr-1. Global export estimates show small variation (typically < 10%) to factor of 2 changes in model parameter values. The model is also robust to the choices of the satellite data products used and enables interannual changes to be quantified. The present synthesis of observations and models provides a path for quantifying the ocean's biological pump.

Impact Of Resolving Submesoscale Features On Modeling The Gulf Stream System

NASA Astrophysics Data System (ADS)

Chassignet, E.; Xu, X.

2016-02-01

Despite being one the best-known circulation pattern of the world ocean, the representation of the Gulf Stream, especially its energetic extension east of the New England Seamounts Chains in the western North Atlantic Ocean, has been a major challenge for ocean general circulation models even at eddy-rich resolutions. Here we show that, for the first time, a simulation of the North Atlantic circulation at 1/50° resolution realistically represents the narrow, energetic jet near 55°W when compared to observations, whereas similarly configured simulations at 1/25° and 1/12° resolution do not. This result highlights the importance of submesoscale features in driving the energetic Gulf Stream extension in the western North Atlantic. The results are discussed in terms of mesoscale and submesoscale energy power spectra.

The Errors Sources Affect to the Results of One-Way Nested Ocean Regional Circulation Model

NASA Astrophysics Data System (ADS)

Pham, S. V.

2016-02-01

Pham-Van Sy1, Jin Hwan Hwang2 and Hyeyun Ku3 Dept. of Civil & Environmental Engineering, Seoul National University, KoreaEmail: 1phamsymt@gmail.com (Corresponding author) Email: 2jinhwang@snu.ac.krEmail: 3hyeyun.ku@gmail.comAbstractThe Oceanic Regional Circulation Model (ORCM) is an essential tool in resolving highly a regional scale through downscaling dynamically the results from the roughly revolved global model. However, when dynamic downscaling from a coarse resolution of the global model or observations to the small scale, errors are generated due to the different sizes of resolution and lateral updating frequency. This research evaluated the effect of four main sources on the results of the ocean regional circulation model (ORCMs) during downscaling and nesting the output data from the ocean global circulation model (OGCMs). Representative four error sources should be the way of the LBC formulation, the spatial resolution difference between driving and driven data, the frequency for up-dating LBCs and domain size. Errors which are contributed from each error source to the results of the ORCMs are investigated separately by applying the Big-Brother Experiment (BBE). Within resolution of 3km grid point of the ORCMs imposing in the BBE framework, it clearly exposes that the simulation results of the ORCMs significantly depend on the domain size and specially the spatial and temporal resolution of lateral boundary conditions (LBCs). The ratio resolution of spatial resolution between driving data and driven model could be up to 3, the updating frequency of the LBCs can be up to every 6 hours per day. The optimal domain size of the ORCMs could be smaller than the OGCMs' domain size around 2 to 10 times. Key words: ORCMs, error source, lateral boundary conditions, domain size Acknowledgement: This research was supported by grants from the Korean Ministry of Oceans and Fisheries entitled as "Developing total management system for the Keum river estuary and coast" and "Development of Technology for CO2 Marine Geological Storage". We also thank to the administrative supports of the Integrated Research Institute of Construction and Environmental Engineering of the Seoul National University.

A thermo-mechanical model of horizontal subduction below an overriding plate

NASA Astrophysics Data System (ADS)

van Hunen, Jeroen; van den Berg, Arie P.; Vlaar, Nico J.

2000-10-01

Subduction of young oceanic lithosphere cannot be explained by the gravitational driving mechanisms of slab pull and ridge push. This deficiency of driving forces can be overcome by obduction of an actively overriding plate, which forces the young plate either to subduct or to collide. This mechanism leads to shallow flattening of the slab as observed today under parts of the west coast of North and South America. Here this process is examined by means of numerical modeling. The convergence velocity between oceanic and continental lithospheric plates is computed from the modeling results, and the ratio of the subduction velocity over the overriding velocity is used as a diagnostic of the efficiency of the ongoing subduction process. We have investigated several factors influencing the mechanical resistance working against the subduction process. In particular, we have studied the effect of a preexisting lithospheric fault with a depth dependent shear resistance, partly decoupling the oceanic lithosphere from the overriding continent. We also investigated the lubricating effect of a 7 km thick basaltic crustal layer on the efficiency of the subduction process and found a log-linear relation between convergence rate and viscosity prefactor characterizing the strength of the oceanic crust, for a range of parameter values including values for basaltic rocks, derived from empirical data. A strong mantle fixes the subducting slab while being overridden and prevents the slab from further subduction in a Benioff style. Viscous heating lowers the coupling strength of the crustal interface between the converging plates with about half an order of magnitude and therefore contributes significantly to the subduction process. Finally, when varying the overriding velocity from 2.5 to 10 cm yr -1, we found a non-linear increase of the subduction velocity due to the presence of non-linear mantle rheology. These results indicate that active obduction of oceanic lithosphere by an overriding continental lithosphere is a viable mechanism for shallow flat subduction over a wide range of model parameters.

75 FR 78654 - Proposed Flood Elevation Determinations

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2010-12-16

... Ocean (entire shoreline of Approximately 1.5 miles None [caret]3 Maui County. the Island of Lanai... [caret]55 southwest of the intersection of Hulopoe Drive and Mauna Lei Drive. Pacific Ocean--Island of Maui....... Southeast corner of the None [caret]4 Maui County. Island of Maui, approximately 670 feet...

77 FR 50016 - Drawbridge Operation Regulation; Grassy Sound Channel, Middle Township, NJ

Federal Register 2010, 2011, 2012, 2013, 2014

2012-08-20

... Operation Regulation; Grassy Sound Channel, Middle Township, NJ AGENCY: Coast Guard, DHS. ACTION: Notice of... operating schedule that governs the Grassy Sound Channel (Ocean Drive) Bridge across the Grassy Sound... operating schedule to accommodate ``The Wild Half'' run. The Grassy Sound Channel (Ocean Drive) Bridge...

Compiled records of carbon isotopes in atmospheric CO2 for historical simulations in CMIP6

NASA Astrophysics Data System (ADS)

Graven, Heather; Allison, Colin E.; Etheridge, David M.; Hammer, Samuel; Keeling, Ralph F.; Levin, Ingeborg; Meijer, Harro A. J.; Rubino, Mauro; Tans, Pieter P.; Trudinger, Cathy M.; Vaughn, Bruce H.; White, James W. C.

2017-12-01

The isotopic composition of carbon (Δ14C and δ13C) in atmospheric CO2 and in oceanic and terrestrial carbon reservoirs is influenced by anthropogenic emissions and by natural carbon exchanges, which can respond to and drive changes in climate. Simulations of 14C and 13C in the ocean and terrestrial components of Earth system models (ESMs) present opportunities for model evaluation and for investigation of carbon cycling, including anthropogenic CO2 emissions and uptake. The use of carbon isotopes in novel evaluation of the ESMs' component ocean and terrestrial biosphere models and in new analyses of historical changes may improve predictions of future changes in the carbon cycle and climate system. We compile existing data to produce records of Δ14C and δ13C in atmospheric CO2 for the historical period 1850-2015. The primary motivation for this compilation is to provide the atmospheric boundary condition for historical simulations in the Coupled Model Intercomparison Project 6 (CMIP6) for models simulating carbon isotopes in the ocean or terrestrial biosphere. The data may also be useful for other carbon cycle modelling activities.

Global Marine Productivity and Living-Phytoplankton Carbon Biomass Estimated from a Physiological Growth Model

NASA Astrophysics Data System (ADS)

Arteaga, L.; Pahlow, M.; Oschlies, A.

2016-02-01

Primay production by marine phytoplankton essentially drives the oceanic biological carbon pump. Global productivity estimates are commonly founded on chlorophyll-based primary production models. However, a major drawback of most of these models is that variations in chlorophyll concentration do not necessarily account for changes in phytoplankton biomass resulting from the physiological regulation of the chlorophyll-to-carbon ratio (Chl:C). Here we present phytoplankton production rates and surface phytoplankton C concentrations for the global ocean for 2005-2010, obtained by combining satellite Chl observations with a mechanistic model for the acclimation of phytoplankton stoichiometry to variations in nutrients, light and temperature. We compare our inferred phytoplankton C concentrations with an independent estimate of surface particulate organic carbon (POC) to identify for the first time the global contribution of living phytoplankton to total POC in the surface ocean. Our annual primary production (46 Pg C yr-1) is in good agreement with other C-based model estimates obtained from satellite observations. We find that most of the oligotrophic surface ocean is dominated by living phytoplankton biomass (between 30-70% of total particulate carbon). Lower contributions are found in the tropical Pacific (10-30% phytoplankton) and the Southern Ocean (≈ 10%). Our method provides a novel analytical tool for identifying changes in marine plankton communities and carbon cycling.

Ocean plankton. Environmental characteristics of Agulhas rings affect interocean plankton transport.

PubMed

Villar, Emilie; Farrant, Gregory K; Follows, Michael; Garczarek, Laurence; Speich, Sabrina; Audic, Stéphane; Bittner, Lucie; Blanke, Bruno; Brum, Jennifer R; Brunet, Christophe; Casotti, Raffaella; Chase, Alison; Dolan, John R; d'Ortenzio, Fabrizio; Gattuso, Jean-Pierre; Grima, Nicolas; Guidi, Lionel; Hill, Christopher N; Jahn, Oliver; Jamet, Jean-Louis; Le Goff, Hervé; Lepoivre, Cyrille; Malviya, Shruti; Pelletier, Eric; Romagnan, Jean-Baptiste; Roux, Simon; Santini, Sébastien; Scalco, Eleonora; Schwenck, Sarah M; Tanaka, Atsuko; Testor, Pierre; Vannier, Thomas; Vincent, Flora; Zingone, Adriana; Dimier, Céline; Picheral, Marc; Searson, Sarah; Kandels-Lewis, Stefanie; Acinas, Silvia G; Bork, Peer; Boss, Emmanuel; de Vargas, Colomban; Gorsky, Gabriel; Ogata, Hiroyuki; Pesant, Stéphane; Sullivan, Matthew B; Sunagawa, Shinichi; Wincker, Patrick; Karsenti, Eric; Bowler, Chris; Not, Fabrice; Hingamp, Pascal; Iudicone, Daniele

2015-05-22

Agulhas rings provide the principal route for ocean waters to circulate from the Indo-Pacific to the Atlantic basin. Their influence on global ocean circulation is well known, but their role in plankton transport is largely unexplored. We show that, although the coarse taxonomic structure of plankton communities is continuous across the Agulhas choke point, South Atlantic plankton diversity is altered compared with Indian Ocean source populations. Modeling and in situ sampling of a young Agulhas ring indicate that strong vertical mixing drives complex nitrogen cycling, shaping community metabolism and biogeochemical signatures as the ring and associated plankton transit westward. The peculiar local environment inside Agulhas rings may provide a selective mechanism contributing to the limited dispersal of Indian Ocean plankton populations into the Atlantic. Copyright © 2015, American Association for the Advancement of Science.

Spaceborne Studies Of Ocean Circulation

NASA Astrophysics Data System (ADS)

Patzert, William C.

1984-08-01

The global view of the oceans seen by Seasat during its 1978 flight demonstrated the feasibility of ocean remote sensing. These first-ever global data sets of sea surface topography (altimeter) and marine winds (scatterometer) laid the foundation for two satellite missions planned for the late 1980's. The future missions are the next generation of altimeter and scatterometer to be flown aboard TOPEX (Topography Experiment) and NROSS (Navy Remote Ocean Sensing System), respectively. The data from these satellites will be coordinated with measurements made at sea to determine the driving forces of ocean circulation and to study the oceans role in climate variability. Sea surface winds (calculated from scatterometer measurements) are the fundamental driving force for ocean waves and currents (estimated from altimeter measurements). On a global scale, the winds and currents are approximately equal partners in redistributing the excess heat gained in the tropics from solar radiation to the cooler polar regions. Small perturbations in this system can dramatically alter global weather, such as the El Niho event of 1982-83. During an El Ni?io event, global wind patterns and ocean currents are perturbed causing unusual ocean warming in the tropical Pacfic Ocean. These ocean events are coupled to complex fluctuations in global weather. Only with satellites will we be able to collect the global data sets needed to study events such as El Ni?o. When TOPEX and NROSS fly, oceanographers will have the equivalent of meteorological high and low pressure charts of ocean topography as well as the surface winds to study ocean "weather." This ability to measure ocean circulation and its driving forces is a critical element in understanding the influence of oceans on society. Climatic changes, fisheries, commerce, waste disposal, and national defense are all involved.

Office of Water Prediction

Science.gov Websites

Toggle navigation National Water Center Home (current) Visualize Map Image Viewer What's New About National Water Center National Water Model National Weather Service National Oceanic and Atmospheric Administration Welcome to the Office of Water Prediction Scientific excellence and innovation driving water

Geothermal influences on the abyssal ocean

NASA Astrophysics Data System (ADS)

Emile-Geay, J.; Madec, G.

2017-12-01

Long considered a negligible contribution to ocean dynamics, geothermal heat flow (GHF) is now increasingly recognized as an important contributor to the large scale ocean's deep structure and circulation. This presentation will review the history of theories regarding geothermal influences on the abyssal ocean. Though the contribution to the thermal structure was recognized early on, its potential in driving a circulation [Worthington, 1968] was largely ignored on the grounds that it could not materially affect potential vorticity. Huang [JPO, 1999] proposed that GHF may provide 30-50% of the energy available for deep mixing, a calculation that later proved too optimistic [Wunsch & Ferrari ARFM 2004]. Model simulations suggested that a uniform GHF of 50 mW/m2 could drive an abyssal of a few Sverdrups (1 Sv = 106 m3.s-1) [Adcroft et al, GRL 2001], but it was not until Emile-Geay & Madec [OS, 2009] (EM09) that GHF began to be taken seriously [Mashayek et al, GRL 2013; Voldoire et al. Clim. Dyn. 2013; Dufresnes et al., Clim. Dyn. 2013]. Using analytical and numerical approaches, the study made 3 main points: GHF brings as much energy to the deep ocean as intense diapycnal mixing (1 cm2/s). GHF consumes the densest water masses, inducing a deep circulation of 5 Sv even without mixing. This circulation varies in inverse proportion to abyssal stratification. The spatial structure of GHF, highest at mid-ocean ridges and lowest in abyssal plains, matters far less than the fact that it bathes vast fractions of the ocean floor in a relatively low, constant flux. EM09 concluded that GHF "is an important actor of abyssal dynamics, and should no longer be neglected in oceanographic studies". Recent work has confirmed that geothermal heat flow is of comparable importance to ocean circulation as bottom-intensified mixing induced by internal wave breaking [De Lavergne et al, JPO 2016a,b]. Thus, including GHF in ocean general circulation models improves abyssal structure and circulation. We conclude with a perspective on the role of conductive geothermal heat loss versus localized, advective hydrothermal heat flow on abyssal dynamics, and delineate unsolved research problems for the years ahead.

Processes controlling surface, bottom and lateral melt of Arctic sea ice in a state of the art sea ice model.

PubMed

Tsamados, Michel; Feltham, Daniel; Petty, Alek; Schroeder, David; Flocco, Daniela

2015-10-13

We present a modelling study of processes controlling the summer melt of the Arctic sea ice cover. We perform a sensitivity study and focus our interest on the thermodynamics at the ice-atmosphere and ice-ocean interfaces. We use the Los Alamos community sea ice model CICE, and additionally implement and test three new parametrization schemes: (i) a prognostic mixed layer; (ii) a three equation boundary condition for the salt and heat flux at the ice-ocean interface; and (iii) a new lateral melt parametrization. Recent additions to the CICE model are also tested, including explicit melt ponds, a form drag parametrization and a halodynamic brine drainage scheme. The various sea ice parametrizations tested in this sensitivity study introduce a wide spread in the simulated sea ice characteristics. For each simulation, the total melt is decomposed into its surface, bottom and lateral melt components to assess the processes driving melt and how this varies regionally and temporally. Because this study quantifies the relative importance of several processes in driving the summer melt of sea ice, this work can serve as a guide for future research priorities. © 2015 The Author(s).

78 FR 48314 - Drawbridge Operation Regulation; Grassy Sound Channel, Middle Township, NJ

Federal Register 2010, 2011, 2012, 2013, 2014

2013-08-08

... Operation Regulation; Grassy Sound Channel, Middle Township, NJ AGENCY: Coast Guard, DHS. ACTION: Notice of... operating schedule that governs the Grassy Sound Channel Bridge (Ocean Drive) across Grassy Sound, mile 1.0..., the Grassy Sound Channel Bridge (Ocean Drive), at mile 1.0, at Middle Township, NJ is open on signal...

Detecting anthropogenic climate forcing in the ocean

NASA Astrophysics Data System (ADS)

Wijffels, S. A.

2016-12-01

Owing to its immense heat capacity, the global ocean is the fly-wheel of the climate system, absorbing, redistributing and storing heat on long timescales and over great distances. Of the extra heat trapped in the Earth System due to rising greenhouse gases, over 90% is being stored in the global oceans. Tracking this warming has been challenging due to past changes in the coverage and technology used in past ocean observations. Here, I'll review progress in estimating past warming rates and patterns. The warming of Earth's surface is also driving changes in the global hydrological cycle, which also intimately involves the oceans. Global ocean salinity changes reveal another footprint of a warming Earth. Some simple model runs that give insight into observed subsurface changes will also be described, along with an update on current warming rates and patterns as tracked by the global Argo programme. The prospects for the next advances in broadscale ocean monitoring will also be discussed.

Arctic pathways of Pacific Water: Arctic Ocean Model Intercomparison experiments.

PubMed

Aksenov, Yevgeny; Karcher, Michael; Proshutinsky, Andrey; Gerdes, Rüdiger; de Cuevas, Beverly; Golubeva, Elena; Kauker, Frank; Nguyen, An T; Platov, Gennady A; Wadley, Martin; Watanabe, Eiji; Coward, Andrew C; Nurser, A J George

2016-01-01

Pacific Water (PW) enters the Arctic Ocean through Bering Strait and brings in heat, fresh water, and nutrients from the northern Bering Sea. The circulation of PW in the central Arctic Ocean is only partially understood due to the lack of observations. In this paper, pathways of PW are investigated using simulations with six state-of-the art regional and global Ocean General Circulation Models (OGCMs). In the simulations, PW is tracked by a passive tracer, released in Bering Strait. Simulated PW spreads from the Bering Strait region in three major branches. One of them starts in the Barrow Canyon, bringing PW along the continental slope of Alaska into the Canadian Straits and then into Baffin Bay. The second begins in the vicinity of the Herald Canyon and transports PW along the continental slope of the East Siberian Sea into the Transpolar Drift, and then through Fram Strait and the Greenland Sea. The third branch begins near the Herald Shoal and the central Chukchi shelf and brings PW into the Beaufort Gyre. In the models, the wind, acting via Ekman pumping, drives the seasonal and interannual variability of PW in the Canadian Basin of the Arctic Ocean. The wind affects the simulated PW pathways by changing the vertical shear of the relative vorticity of the ocean flow in the Canada Basin.

Coupled ocean-shelf ecosystem modelling of northern North Atlantic

NASA Astrophysics Data System (ADS)

Harle, J.; Holt, J. T.; Butenschön, M.; Allen, J. I.

2016-02-01

The biogeochemistry and ecosystems of the open-ocean and shelf seas are intimately connected. For example Northwest European continental shelf receives a substantial fraction of its nutrients from the wider North Atlantic and exports carbon at depth, sequestering it from atmospheric exchange. In the EC FP7 EuroBasin project (Holt et al 2014) we have developed a 1/12 degree basin-scale NEMO-ERSEM model with specific features relevant to shelf seas (e.g. tides and advanced vertical mixing schemes). This model is eddy resolving in the open-ocean, and resolves barotropic scales on-shelf. We use this model to explore the interaction between finely resolved physical processes and the ecosystem. Here we focus on shelf-sea processes and the connection between the shelf seas and open-ocean, and compare results with a 1/4 degree (eddy permitting) model that does not include shelf sea processes. We find tidal mixing fronts and river plume are well represented in the 1/12 degree model. Using approaches developed for the NW Shelf (Holt et al 2012), we provide estimates of across-shelf break nutrient fluxes to the seas surrounding this basin, and relate these fluxes and their interannual variability to the physical processes driving ocean-shelf exchange. Holt, J., et al, 2012. Oceanic controls on the primary production of the northwest European continental shelf: model experiments under recent past conditions and a potential future scenario. Biogeosciences 9, 97-117. Holt, J., et al, 2014. Challenges in integrative approaches to modelling the marine ecosystems of the North Atlantic: Physics to Fish and Coasts to Ocean. Progress in Oceanography doi:10.1016/j.pocean.2014.04.024.

Remote forcing at the Last Glacial Maximum in the Tropical Pacific Ocean

NASA Astrophysics Data System (ADS)

Andreasen, Dyke H.; Ravelo, A. Christina; Broccoli, Anthony J.

2001-01-01

We present results of a Last Glacial Maximum (LGM) wind stress sensitivity experiment using a high-resolution ocean general circulation model of the tropical Pacific Ocean. LGM wind stress, used to drive the ocean model, was generated using an atmospheric general circulation model simulation forced by LGM boundary conditions as part of the Paleoclimate Modeling Intercomparison Project (PMIP) [Broccoli, 2000]. LGM wind stress anomalies were large in the western half of the basin, yet there was a significant hydrographic response in the eastern half. This ocean model experiment hind casts changes that are in close agreement with paleoceanographic data from the entire region, even without the explicit modeling of the air-sea interactions. Data and model both predict that the annual average thermocline tilt across the basin was enhanced. Data and model are consistent with a stronger equatorial undercurrent which shoaled to the west of where it does today, and stronger advection of water from the Peru Current into the east equatorial Pacific and across the equator. Paleoproductivity and sea surface temperature (SST) data are interpreted in light of the modeling results, indicating that paleoproductivity changes were related to wind-forced dynamical changes resulting from LGM boundary conditions, while SST changes were related to independent, possibly radiative, forcing. Overall, our results imply that much of the dynamic response of the tropical Pacific during the LGM can be explained by wind field changes resulting from global LGM boundary conditions.

A numerical investigation of continental collision styles

NASA Astrophysics Data System (ADS)

Ghazian, Reza Khabbaz; Buiter, Susanne J. H.

2013-06-01

Continental collision after closure of an ocean can lead to different deformation styles: subduction of continental crust and lithosphere, lithospheric thickening, folding of the unsubducted continents, Rayleigh-Taylor (RT) instabilities and/or slab break-off. We use 2-D thermomechanical models of oceanic subduction followed by continental collision to investigate the sensitivity of these collision styles to driving velocity, crustal and lithospheric temperature, continental rheology and the initial density difference between the oceanic lithosphere and the asthenosphere. We find that these parameters influence the collision system, but that driving velocity, rheology and lithospheric (rather than Moho and mantle) temperature can be classified as important controls, whereas reasonable variations in the initial density contrast between oceanic lithosphere and asthenosphere are not necessarily important. Stable continental subduction occurs over a relatively large range of values of driving velocity and lithospheric temperature. Fast and cold systems are more likely to show folding, whereas slow and warm systems can experience RT-type dripping. Our results show that a continent with a strong upper crust can experience subduction of the entire crust and is more likely to fold. Accretion of the upper crust at the trench is feasible when the upper crust has a moderate to weak strength, whereas the entire crust can be scraped-off in the case of a weak lower crust. We also illustrate that weakening of the lithospheric mantle promotes RT-type of dripping in a collision system. We use a dynamic collision model, in which collision is driven by slab pull only, to illustrate that adjacent plates can play an important role in continental collision systems. In dynamic collision models, exhumation of subducted continental material and sediments is triggered by slab retreat and opening of a subduction channel, which allows upward flow of buoyant materials. Exhumation continues after slab break-off by reverse motion of the subducting plate (`eduction') caused by the reduced slab pull. We illustrate how a simple force balance of slab pull, slab push, slab bending, viscous resistance and buoyancy can explain the different collision styles caused by variations in velocity, temperature, rheology, density differences and the interaction with adjacent plates.

Mechanisms driving variability in the ocean forcing of Pine Island Glacier

PubMed Central

Webber, Benjamin G. M.; Heywood, Karen J.; Stevens, David P.; Dutrieux, Pierre; Abrahamsen, E. Povl; Jenkins, Adrian; Jacobs, Stanley S.; Ha, Ho Kyung; Lee, Sang Hoon; Kim, Tae Wan

2017-01-01

Pine Island Glacier (PIG) terminates in a rapidly melting ice shelf, and ocean circulation and temperature are implicated in the retreat and growing contribution to sea level rise of PIG and nearby glaciers. However, the variability of the ocean forcing of PIG has been poorly constrained due to a lack of multi-year observations. Here we show, using a unique record close to the Pine Island Ice Shelf (PIIS), that there is considerable oceanic variability at seasonal and interannual timescales, including a pronounced cold period from October 2011 to May 2013. This variability can be largely explained by two processes: cumulative ocean surface heat fluxes and sea ice formation close to PIIS; and interannual reversals in ocean currents and associated heat transport within Pine Island Bay, driven by a combination of local and remote forcing. Local atmospheric forcing therefore plays an important role in driving oceanic variability close to PIIS. PMID:28211473

77 FR 30261 - Petition To List 83 Species of Coral as Threatened or Endangered Under the Endangered Species Act...

Federal Register 2010, 2011, 2012, 2013, 2014

2012-05-22

... Center, Center of Excellence in Coral Reef Ecosystems Science, 8000 North Ocean Drive; Dania Beach, FL... Center, Center of Excellence in Coral Reef Ecosystems Science, 8000 North Ocean Drive, Dania Beach, FL... science workshops will focus on two themes: ``Climate Change and Climate Impacts on Coral Reef Ecosystems...

Nano-tags for neonates and ocean-mediated swimming behaviours linked to rapid dispersal of hatchling sea turtles

PubMed Central

Scott, Rebecca; Biastoch, Arne; Roder, Christian; Stiebens, Victor A.; Eizaguirre, Christophe

2014-01-01

Dispersal during juvenile life stages drives the life-history evolution and dynamics of many marine vertebrate populations. However, the movements of juvenile organisms, too small to track using conventional satellite telemetry devices, remain enigmatic. For sea turtles, this led to the paradigm of the ‘lost years' since hatchlings disperse widely with ocean currents. Recently, advances in the miniaturization of tracking technology have permitted the application of nano-tags to track cryptic organisms. Here, the novel use of acoustic nano-tags on neonate loggerhead turtle hatchlings enabled us to witness first-hand their dispersal and behaviour during their first day at sea. We tracked hatchlings distances of up to 15 km and documented their rapid transport (up to 60 m min−1) with surface current flows passing their natal areas. Tracking was complemented with laboratory observations to monitor swimming behaviours over longer periods which highlighted (i) a positive correlation between swimming activity levels and body size and (ii) population-specific swimming behaviours (e.g. nocturnal inactivity) suggesting local oceanic conditions drive the evolution of innate swimming behaviours. Knowledge of the swimming behaviours of small organisms is crucial to improve the accuracy of ocean model simulations used to predict the fate of these organisms and determine resultant population-level implications into adulthood. PMID:25339720

Atmospheric and Oceanic Response to Southern Ocean Deep Convection Oscillations on Decadal to Centennial Time Scales in Climate Models

NASA Astrophysics Data System (ADS)

Martin, T.; Reintges, A.; Park, W.; Latif, M.

2014-12-01

Many current coupled global climate models simulate open ocean deep convection in the Southern Ocean as a recurring event with time scales ranging from a few years to centennial (de Lavergne et al., 2014, Nat. Clim. Ch.). The only observation of such event, however, was the occurrence of the Weddell Polynya in the mid-1970s, an open water area of 350 000 km2 within the Antarctic sea ice in three consecutive winters. Both the wide range of modeled frequency of occurrence and the absence of deep convection in the Weddell Sea highlights the lack of understanding concerning the phenomenon. Nevertheless, simulations indicate that atmospheric and oceanic responses to the cessation of deep convection in the Southern Ocean include a strengthening of the low-level atmospheric circulation over the Southern Ocean (increasing SAM index) and a reduction in the export of Antarctic Bottom Water (AABW), potentially masking the regional effects of global warming (Latif et al., 2013, J. Clim.; Martin et al., 2014, Deep Sea Res. II). It is thus of great importance to enhance our understanding of Southern Ocean deep convection and clarify the associated time scales. In two multi-millennial simulations with the Kiel Climate Model (KCM, ECHAM5 T31 atmosphere & NEMO-LIM2 ~2˚ ocean) we showed that the deep convection is driven by strong oceanic warming at mid-depth periodically overriding the stabilizing effects of precipitation and ice melt (Martin et al., 2013, Clim. Dyn.). Sea ice thickness also affects location and duration of the deep convection. A new control simulation, in which, amongst others, the atmosphere grid resolution is changed to T42 (~2.8˚), yields a faster deep convection flip-flop with a period of 80-100 years and a weaker but still significant global climate response similar to CMIP5 simulations. While model physics seem to affect the time scale and intensity of the phenomenon, the driving mechanism is a rather robust feature. Finally, we compare the atmospheric and oceanic responses among CMIP5 models. Since open ocean convection is the dominant mode of AABW formation in these models, the northward extent and strength of the AABW cell in the Atlantic correlates with the deep convection intensity but varies between models. Likewise, atmospheric response patterns outside the Southern Ocean region are not consistent among models.

Climate-driven polar motion

NASA Astrophysics Data System (ADS)

Celaya, Michael A.; Wahr, John M.; Bryan, Frank O.

1999-06-01

The output of a coupled climate system model provides a synthetic climate record with temporal and spatial coverage not attainable with observational data, allowing evaluation of climatic excitation of polar motion on timescales of months to decades. Analysis of the geodetically inferred Chandler excitation power shows that it has fluctuated by up to 90% since 1900 and that it has characteristics representative of a stationary Gaussian process. Our model-predicted climate excitation of the Chandler wobble also exhibits variable power comparable to the observed. Ocean currents and bottom pressure shifts acting together can alone drive the 14-month wobble. The same is true of the excitation generated by the combined effects of barometric pressure and winds. The oceanic and atmospheric contributions are this large because of a relatively high degree of constructive interference between seafloor pressure and currents and between atmospheric pressure and winds. In contrast, excitation by the redistribution of water on land appears largely insignificant. Not surprisingly, the full climate effect is even more capable of driving the wobble than the effects of the oceans or atmosphere alone are. Our match to the observed annual excitation is also improved, by about 17%, over previous estimates made with historical climate data. Efforts to explain the 30-year Markowitz wobble meet with less success. Even so, at periods ranging from months to decades, excitation generated by a model of a coupled climate system makes a close approximation to the amplitude of what is geodetically observed.

Mesoscale Effects on Carbon Export: A Global Perspective

NASA Astrophysics Data System (ADS)

Harrison, Cheryl S.; Long, Matthew C.; Lovenduski, Nicole S.; Moore, Jefferson K.

2018-04-01

Carbon export from the surface to the deep ocean is a primary control on global carbon budgets and is mediated by plankton that are sensitive to physical forcing. Earth system models generally do not resolve ocean mesoscale circulation (O(10-100) km), scales that strongly affect transport of nutrients and plankton. The role of mesoscale circulation in modulating export is evaluated by comparing global ocean simulations conducted at 1° and 0.1° horizontal resolution. Mesoscale resolution produces a small reduction in globally integrated export production (<2%) however, the impact on local export production can be large (±50%), with compensating effects in different ocean basins. With mesoscale resolution, improved representation of coastal jets block off-shelf transport, leading to lower export in regions where shelf-derived nutrients fuel production. Export is further reduced in these regions by resolution of mesoscale turbulence, which restricts the spatial area of production. Maximum mixed layer depths are narrower and deeper across the Subantarctic at higher resolution, driving locally stronger nutrient entrainment and enhanced summer export production. In energetic regions with seasonal blooms, such as the Subantarctic and North Pacific, internally generated mesoscale variability drives substantial interannual variation in local export production. These results suggest that biogeochemical tracer dynamics show different sensitivities to transport biases than temperature and salinity, which should be considered in the formulation and validation of physical parameterizations. Efforts to compare estimates of export production from observations and models should account for large variability in space and time expected for regions strongly affected by mesoscale circulation.

Arctic pathways of Pacific Water: Arctic Ocean Model Intercomparison experiments

PubMed Central

Karcher, Michael; Proshutinsky, Andrey; Gerdes, Rüdiger; de Cuevas, Beverly; Golubeva, Elena; Kauker, Frank; Nguyen, An T.; Platov, Gennady A.; Wadley, Martin; Watanabe, Eiji; Coward, Andrew C.; Nurser, A. J. George

2016-01-01

Abstract Pacific Water (PW) enters the Arctic Ocean through Bering Strait and brings in heat, fresh water, and nutrients from the northern Bering Sea. The circulation of PW in the central Arctic Ocean is only partially understood due to the lack of observations. In this paper, pathways of PW are investigated using simulations with six state‐of‐the art regional and global Ocean General Circulation Models (OGCMs). In the simulations, PW is tracked by a passive tracer, released in Bering Strait. Simulated PW spreads from the Bering Strait region in three major branches. One of them starts in the Barrow Canyon, bringing PW along the continental slope of Alaska into the Canadian Straits and then into Baffin Bay. The second begins in the vicinity of the Herald Canyon and transports PW along the continental slope of the East Siberian Sea into the Transpolar Drift, and then through Fram Strait and the Greenland Sea. The third branch begins near the Herald Shoal and the central Chukchi shelf and brings PW into the Beaufort Gyre. In the models, the wind, acting via Ekman pumping, drives the seasonal and interannual variability of PW in the Canadian Basin of the Arctic Ocean. The wind affects the simulated PW pathways by changing the vertical shear of the relative vorticity of the ocean flow in the Canada Basin. PMID:27818853

The Oceanic Contribution to Atlantic Multi-Decadal Variability

NASA Astrophysics Data System (ADS)

Wills, R. C.; Armour, K.; Battisti, D. S.; Hartmann, D. L.

2017-12-01

Atlantic multi-decadal variability (AMV) is typically associated with variability in ocean heat transport (OHT) by the Atlantic Meridional Overturning Circulation (AMOC). However, recent work has cast doubt on this connection by showing that slab-ocean climate models, in which OHT cannot vary, exhibit similar variability. Here, we apply low-frequency component analysis to isolate the variability of Atlantic sea-surface temperatures (SSTs) that occurs on decadal and longer time scales. In observations and in pre-industrial control simulations of comprehensive climate models, we find that AMV is confined to the extratropics, with the strongest temperature anomalies in the North Atlantic subpolar gyre. We show that warm subpolar temperatures are associated with a strengthened AMOC, increased poleward OHT, and local heat fluxes from the ocean into the atmosphere. In contrast, the traditional index of AMV based on the basin-averaged SST anomaly shows warm temperatures preceded by heat fluxes from the atmosphere into the ocean, consistent with the atmosphere driving this variability, and shows a weak relationship with AMOC. The autocorrelation time of the basin-averaged SST index is 1 year compared to an autocorrelation time of 5 years for the variability of subpolar temperatures. This shows that multi-decadal variability of Atlantic SSTs is sustained by OHT variability associated with AMOC, while atmosphere-driven SST variability, such as exists in slab-ocean models, contributes primarily on interannual time scales.

Impacts of Interactive Stratospheric Chemistry on Antarctic and Southern Ocean Climate Change in the Goddard Earth Observing System Version 5 (GEOS-5)

NASA Technical Reports Server (NTRS)

Li, Feng; Vikhliaev, Yury V.; Newman, Paul A.; Pawson, Steven; Perlwitz, Judith; Waugh, Darryn W.; Douglass, Anne R.

2016-01-01

Stratospheric ozone depletion plays a major role in driving climate change in the Southern Hemisphere. To date, many climate models prescribe the stratospheric ozone layer's evolution using monthly and zonally averaged ozone fields. However, the prescribed ozone underestimates Antarctic ozone depletion and lacks zonal asymmetries. In this study we investigate the impact of using interactive stratospheric chemistry instead of prescribed ozone on climate change simulations of the Antarctic and Southern Ocean. Two sets of 1960-2010 ensemble transient simulations are conducted with the coupled ocean version of the Goddard Earth Observing System Model, version 5: one with interactive stratospheric chemistry and the other with prescribed ozone derived from the same interactive simulations. The model's climatology is evaluated using observations and reanalysis. Comparison of the 1979-2010 climate trends between these two simulations reveals that interactive chemistry has important effects on climate change not only in the Antarctic stratosphere, troposphere, and surface, but also in the Southern Ocean and Antarctic sea ice. Interactive chemistry causes stronger Antarctic lower stratosphere cooling and circumpolar westerly acceleration during November-December-January. It enhances stratosphere-troposphere coupling and leads to significantly larger tropospheric and surface westerly changes. The significantly stronger surface wind stress trends cause larger increases of the Southern Ocean Meridional Overturning Circulation, leading to year-round stronger ocean warming near the surface and enhanced Antarctic sea ice decrease.

Understanding the Role of Air-Sea Interaction on Extreme Rainfall in Aquaplanet and Earth-like CESM2

NASA Astrophysics Data System (ADS)

Benedict, J. J.; Clement, A. C.; Medeiros, B.

2017-12-01

Extreme precipitation events are associated with anomalous, latitudinally dependent dynamical and convective weather systems. For example, plumes of excessive poleward water vapor transport and topographical effects drive extreme precipitation events in the midlatitudes, while intense tropical precipitation is associated with organized convective systems. In both cases, air-sea fluxes have the potential to contribute significantly to the moisture budget of these storms, but the roles of surface fluxes and upper-ocean processes and their impact on precipitation extremes have yet to be explored in sufficient detail. To examine such mechanisms, we implement a climate model hierarchy that encompasses a spectrum of ocean models, from prescribed-SST to fully dynamic, as well as both aquaplanet and Earth-like lower boundary types within version 2 of the Community Earth System Model (CESM2). Using the CESM2 hierarchy and comparing to observations, we identify key moisture processes and related air-sea interactions that drive extreme precipitation events across different latitudes in Earth-like models and then generalize the analyses in aquaplanet configurations to highlight the most salient features. The analyses are applied to both present-day and global warming conditions to investigate how these fundamental mechanisms might change extreme precipitation events in the future climate.

Expanded oxygen minimum zones during the late Paleocene-early Eocene: Hints from multiproxy comparison and ocean modeling

NASA Astrophysics Data System (ADS)

Zhou, X.; Thomas, E.; Winguth, A. M. E.; Ridgwell, A.; Scher, H.; Hoogakker, B. A. A.; Rickaby, R. E. M.; Lu, Z.

2016-12-01

Anthropogenic warming could well drive depletion of oceanic oxygen in the future. Important insight into the relationship between deoxygenation and warming can be gleaned from the geological record, but evidence is limited because few ocean oxygenation records are available for past greenhouse climate conditions. We use I/Ca in benthic foraminifera to reconstruct late Paleocene through early Eocene bottom and pore water redox conditions in the South Atlantic and Southern Indian Oceans and compare our results with those derived from Mn speciation and the Ce anomaly in fish teeth. We conclude that waters with lower oxygen concentrations were widespread at intermediate depths (1.5-2 km), whereas bottom waters were more oxygenated at the deepest site, in the Southeast Atlantic Ocean (>3 km). Epifaunal benthic foraminiferal I/Ca values were higher in the late Paleocene, especially at low-oxygen sites, than at well-oxygenated modern sites, indicating higher seawater total iodine concentrations in the late Paleocene than today. The proxy-based bottom water oxygenation pattern agrees with the site-to-site O2 gradient as simulated in a comprehensive climate model (Community Climate System Model Version 3), but the simulated absolute dissolved O2 values are low (< 35 µmol/kg), while higher O2 values ( 60-100 µmol/kg) were obtained in an Earth system model (Grid ENabled Integrated Earth system model). Multiproxy data together with improvements in boundary conditions and model parameterization are necessary if the details of past oceanographic oxygenation are to be resolved.

Tropical cloud feedbacks and natural variability of climate

NASA Technical Reports Server (NTRS)

Miller, R. L.; Del Genio, A. D.

1994-01-01

Simulations of natural variability by two general circulation models (GCMs) are examined. One GCM is a sector model, allowing relatively rapid integration without simplification of the model physics, which would potentially exclude mechanisms of variability. Two mechanisms are found in which tropical surface temperature and sea surface temperature (SST) vary on interannual and longer timescales. Both are related to changes in cloud cover that modulate SST through the surface radiative flux. Over the equatorial ocean, SST and surface temperature vary on an interannual timescale, which is determined by the magnitude of the associated cloud cover anomalies. Over the subtropical ocean, variations in low cloud cover drive SST variations. In the sector model, the variability has no preferred timescale, but instead is characterized by a 'red' spectrum with increasing power at longer periods. In the terrestrial GCM, SST variability associated with low cloud anomalies has a decadal timescale and is the dominant form of global temperature variability. Both GCMs are coupled to a mixed layer ocean model, where dynamical heat transports are prescribed, thus filtering out El Nino-Southern Oscillation (ENSO) and thermohaline circulation variability. The occurrence of variability in the absence of dynamical ocean feedbacks suggests that climatic variability on long timescales can arise from atmospheric processes alone.

Global Warming In A Regional Model of The Atlantic Ocean - Echam4/opyc3 In Flame 4/3

NASA Astrophysics Data System (ADS)

Schweckendiek, U.; Willebrand, J.

The reaction of the Thermohaline Circulation (THC) in most climate models on global warming scenarios is a weakening of the THC. An exception is the ECHAM4/OPYC3 simulation whose stable behaviour is traced back to a strongly enhanced evaporation and as a consequence to a development of a salt anomaly in the tropics and subtropics of the Atlantic Ocean (Latif et al.,2000). This salt signal is advected into convection regions and compensates the reduction of surface density due to surface heating and freshening. To examine this scenario for a more realistic ocean model, data from this model is used to drive a reginal model of the Atlantic Ocean. In order to test the crucial mechanisms for the maintainance of the meridional overturning, we have performed sensitivity studies by focussing on different combinations of the anomalous freshwater and heat fluxes. The results demonstrate that for the stabilising effect to become effective the salt sig- nal has to enter the GIN-Seas and subsequently the overflow waters, underlining the importance of the overflows for the THC. The Labrador Sea Convection is however uneffected by this stabilising salt signal and its convection ultimatly breaks down un- der surface warming and freshening.

Southern Ocean Open Ocean Polynyas in Observations and from a Low- and a High-Resolution Fully-Coupled Earth System Model Simulation

NASA Astrophysics Data System (ADS)

Veneziani, C.; Kurtakoti, P. K.; Weijer, W.; Stoessel, A.

2016-12-01

In contrast to their better known coastal counterpart, open ocean polynyas (OOPs) form through complex driving mechanisms, involving pre-conditioning of the water column, external forcing and internal ocean dynamics, and are therefore much more elusive and less predictable than coastal polynyas. Yet, their impact on bottom water formation and the Meridional Overturning Circulation could prove substantial. Here, we characterize the formation of Southern Ocean OOPs by analyzing the full satellite NASA microwave imager and radiometer (SSMI/SMMR) data record from 1972 to present day. We repeat the same analysis within the low-resolution (LR) and high-resolution (HR) fully-coupled Earth System Model simulations that are part of the Accelerated Climate Model for Energy (ACME) v0 baseline experiments. The focus is on two OOPs that are more consistently seen in observations: the Maud Rise and the Weddell Sea polynyas. Results show that the LR simulation is unable to reproduce any OOP over the 195 years of its duration, while both Maud Rise and Weddell Sea polynyas are seen in the HR simulation, with extents similar to observations'. We explore possible mechanisms that would explain the asymmetric behavior, including topographic processes, eddy shedding events, and different water column stratification between the two simulations.

Modeling water mass formation in the Mertz Glacier Polynya and Adélie Depression, East Antarctica

NASA Astrophysics Data System (ADS)

Marsland, S. J.; Bindoff, N. L.; Williams, G. D.; Budd, W. F.

2004-11-01

High rates of sea ice growth and brine rejection in the Mertz Glacier Polynya drive the production of dense continental shelf waters in the Adélie Depression. We consider the rate of outflow of waters having sufficient density to sink into the neighboring abyssal ocean and form Adélie Land Bottom Water (ALBW). Along with Weddell and Ross Sea Bottom Waters, the ALBW is an important source of Antarctic Bottom Water. The relevant processes are modeled using a variant of the Max Planck Institute Ocean Model (MPIOM) under daily NCEP-NCAR reanalysis forcing for the period 1991-2000. The orthogonal curvilinear horizontal grid allows for the construction of a global domain with high resolution in our region of interest. The modeled Mertz Glacier Polynya is realistic in location and extent, exhibiting low ice thickness (<0.4 m) and low ice fraction (<50%). The net surface ocean to atmosphere heat flux exceeds 200 W m2 and is dominated by sensible heat exchange. In wintertime (May through September inclusive), 7.5 m of sea ice forms over the Adélie Depression at a rate of 4.9 cm d-1: this results in annual average volumetric production of 99 km3 of sea ice. The associated brine release drives dense shelf water formation. The off-shelf flow of dense water exhibits strong interannual variability in response to variability in both atmospheric forcing and ocean preconditioning. Averaged over the period 1991-2000 the off shelf flow of dense water is 0.15 Sv: for a period of strong outflow (1993-1997), this increases to 0.24 Sv. Most of the outflow occurs during July through October, at a rate of 0.40 (0.63) Sv over the period 1991-2000 (1993-1997). The peak mean monthly outflow can exceed 1 Sv.

The Role of External Inputs and Internal Cycling in Shaping the Global Ocean Cobalt Distribution: Insights From the First Cobalt Biogeochemical Model

NASA Astrophysics Data System (ADS)

Tagliabue, Alessandro; Hawco, Nicholas J.; Bundy, Randelle M.; Landing, William M.; Milne, Angela; Morton, Peter L.; Saito, Mak A.

2018-04-01

Cobalt is an important micronutrient for ocean microbes as it is present in vitamin B12 and is a co-factor in various metalloenzymes that catalyze cellular processes. Moreover, when seawater availability of cobalt is compared to biological demands, cobalt emerges as being depleted in seawater, pointing to a potentially important limiting role. To properly account for the potential biological role for cobalt, there is therefore a need to understand the processes driving the biogeochemical cycling of cobalt and, in particular, the balance between external inputs and internal cycling. To do so, we developed the first cobalt model within a state-of-the-art three-dimensional global ocean biogeochemical model. Overall, our model does a good job in reproducing measurements with a correlation coefficient of >0.7 in the surface and >0.5 at depth. We find that continental margins are the dominant source of cobalt, with a crucial role played by supply under low bottom-water oxygen conditions. The basin-scale distribution of cobalt supplied from margins is facilitated by the activity of manganese-oxidizing bacteria being suppressed under low oxygen and low temperatures, which extends the residence time of cobalt. Overall, we find a residence time of 7 and 250 years in the upper 250 m and global ocean, respectively. Importantly, we find that the dominant internal resupply process switches from regeneration and recycling of particulate cobalt to dissolution of scavenged cobalt between the upper ocean and the ocean interior. Our model highlights key regions of the ocean where biological activity may be most sensitive to cobalt availability.

Global Models of Ridge-Push Force, Geoid, and Lithospheric Strength of Oceanic plates

NASA Astrophysics Data System (ADS)

Mahatsente, Rezene

2017-12-01

An understanding of the transmission of ridge-push related stresses in the interior of oceanic plates is important because ridge-push force is one of the principal forces driving plate motion. Here, I assess the transmission of ridge-push related stresses in oceanic plates by comparing the magnitude of the ridge-push force to the integrated strength of oceanic plates. The strength is determined based on plate cooling and rheological models. The strength analysis includes low-temperature plasticity (LTP) in the upper mantle and assumes a range of possible tectonic conditions and rheology in the plates. The ridge-push force has been derived from the thermal state of oceanic lithosphere, seafloor depth and crustal age data. The results of modeling show that the transmission of ridge-push related stresses in oceanic plates mainly depends on rheology and predominant tectonic conditions. If a lithosphere has dry rheology, the estimated strength is higher than the ridge-push force at all ages for compressional tectonics and at old ages (>75 Ma) for extension. Therefore, under such conditions, oceanic plates may not respond to ridge-push force by intraplate deformation. Instead, the plates may transmit the ridge-push related stress in their interior. For a wet rheology, however, the strength of young lithosphere (<75 Ma) is much less than the ridge-push force for both compressional and extensional tectonics. In this case, the ridge-push related stress may dissipate in the interior of oceanic plates and diffuses by intraplate deformation. The state of stress within a plate depends on the balance of far-field and intraplate forces.

Keeping the ocean warm

NASA Astrophysics Data System (ADS)

Nimmo, Francis

2017-12-01

More than 20 GW of power are necessary to balance the heat emitted by Enceladus and avoid the freezing of its internal ocean. A very porous core undergoing tidal heating can generate the required power to maintain a liquid ocean and drive hydrothermal activity.

A 7.5-Year Dataset of SSM/I-Derived Surface Turbulent Fluxes Over Global Oceans

NASA Technical Reports Server (NTRS)

Chou, Shu-Hsien; Shie, Chung-Lin; Atlas, Robert M.; Adizzone, Joe; Nelkin, Eric; Starr, David OC. (Technical Monitor)

2001-01-01

The global air-sea turbulent fluxes are needed for driving ocean models and validating coupled ocean-atmosphere global models. A method was developed to retrieve surface air humidity from the radiances measured by the Special Sensor Microwave/Imager (SSM/I) Using both SSM/I-retrieved surface wind and air humidity, they computed daily turbulent fluxes over global oceans with a stability-dependent bulk scheme. Based on this method, we have produced Version 1 of Goddard Satellite-Based Surface Turbulent Fluxes (GSSTF) dataset from the SSM/I data and other data. It provides daily- and monthly-mean surface turbulent fluxes and some relevant parameters over global oceans for individual F8, F10, and F11 satellites covering the period July 1987-December 1994. It also provides 1988-94 annual- and monthly-mean climatologies of the same variables, using only F8 and F1 1 satellite data. It has a spatial resolution of 2.0 degrees x 2.5 degrees lat-long and is archived at the NASA/GSFC DAAC. The purpose of this paper is to present an updated assessment of the GSSTF 1.0 dataset.

Finding the missing plastic -resolving the global mass (im)balance for plastic pollution in the ocean

NASA Astrophysics Data System (ADS)

Wilcox, C.; van Sebille, E.

2016-02-01

Several global studies have attempted to estimate the standing stock of plastic debris in the oceans at the global scale. However, recent work estimating the amount lost from land on an annual basis suggests that the standing stock should be several orders of magnitude larger than the global estimates. We investigate the role of coastal deposition within the first few weeks after plastic enters the ocean and very near its sources, one of the hypothesized sinks for the missing plastic in this mass balance. We utilize a continental scale dataset of plastics collected along Australia's coast and in the offshore regions together with models of plastic release and transport based on Lagrangian tracking to investigate the role of local deposition in the coastal environment. Our models predict that the vast majority of positively buoyant plastic is deposited within a very short distance from its release point, with only a small fraction escaping into the open ocean. These predictions match our coastal and offshore observations, providing clear evidence that this mechanism of immediate coastal deposition is, at least in part, driving the apparent mismatch between coastal emissions and the standing stock in the ocean.

Deep Water Ocean Acoustics

DTIC Science & Technology

2016-08-03

Militia Drive Lexington, MA 02421 Date Submitted: Aug 3, 2016 Notices : Distribution Statement A. Approved for public release...distribution is unlimited. OASIS, INC. 2 Report No. QSR-14C0172-Ocean Acoustics-063016 Contents Notices ...the impact of the ocean and seafloor environmental variability on deep-water (long-range) ocean acoustic propagation and to develop methodologies

Interagency Working Group on Ocean Social Science: Incorporating ecosystem services approaches into ocean and coastal decision-making and governance

EPA Science Inventory

The application of social science has been recognized as a priority for effective ocean and coastal management, driving much discussion and fostering emerging efforts in several areas. The Interagency Working Group on Ocean Social Science (IWG-OSS) is tasked with assisting the Su...

The Sensitivity of the Greenland Ice Sheet to Glacial-Interglacial Oceanic Forcing

NASA Astrophysics Data System (ADS)

Tabone, I.; Blasco Navarro, J.; Robinson, A.; Alvarez-Solas, J.; Montoya, M.

2017-12-01

Up to now, the scientific community has mainly focused on the sensitivity of the Greenland Ice Sheet (GrIS) to atmospheric variations. However, several studies suggest that the enhanced ice mass loss experienced by the GrIS in the past decades is directly connected to the increasing North Atlantic temperatures. Melting of GrIS outlet glaciers triggers grounding-line retreat increasing ice discharge into the ocean. This new evidence leads to consider the ocean as a relevant driver to be taken into account when modeling the evolution of the GrIS. The ice-ocean interaction is a primary factor controling not only the likely future retreat of GrIS outlet glaciers, or the huge ice loss in past warming climates, but also, and more strongly, the past GrIS glacial expansion. The latter assumption is supported by reconstructions which propose the GrIS to be fully marine-based during glacials, and thus more exposed to the influence of the ocean. Here, for the first time, we investigate the response of the GrIS to past oceanic changes using a three-dimensional hybrid ice-sheet/ice-shelf model, which combines the Shallow Ice Approximation (SIA) for slow grounded ice sheets and the Shallow Shelf Approximation (SSA) in ice shelves and ice streams. The model accounts for a time-dependent parametrisation of the marine basal melting rate, which is used to reproduce past oceanic variations. In this work simulations of the last two glacial cycles are performed. Our results show that the GrIS is very sensitive to the ocean-triggered submarine melting (freezing). Mild oceanic temperature variations lead to a rapid retreat (expansion) of the GrIS margins, which, inducing a dynamic adjustment of the grounded ice sheet, drive the evolution of the whole ice sheet. Our results strongly suggest the need to consider the ocean as an active forcing in paleo ice sheet models.

Intensified Indian Ocean climate variability during the Last Glacial Maximum

NASA Astrophysics Data System (ADS)

Thirumalai, K.; DiNezro, P.; Tierney, J. E.; Puy, M.; Mohtadi, M.

2017-12-01

Climate models project increased year-to-year climate variability in the equatorial Indian Ocean in response to greenhouse gas warming. This response has been attributed to changes in the mean climate of the Indian Ocean associated with the zonal sea-surface temperature (SST) gradient. According to these studies, air-sea coupling is enhanced due to a stronger SST gradient driving anomalous easterlies that shoal the thermocline in the eastern Indian Ocean. We propose that this relationship between the variability and the zonal SST gradient is consistent across different mean climate states. We test this hypothesis using simulations of past and future climate performed with the Community Earth System Model Version 1 (CESM1). We constrain the realism of the model for the Last Glacial Maximum (LGM) where CESM1 simulates a mean climate consistent with a stronger SST gradient, agreeing with proxy reconstructions. CESM1 also simulates a pronounced increase in seasonal and interannual variability. We develop new estimates of climate variability on these timescales during the LGM using δ18O analysis of individual foraminifera (IFA). IFA data generated from four different cores located in the eastern Indian Ocean indicate a marked increase in δ18O-variance during the LGM as compared to the late Holocene. Such a significant increase in the IFA-δ18O variance strongly supports the modeling simulations. This agreement further supports the dynamics linking year-to-year variability and an altered SST gradient, increasing our confidence in model projections.

Role of atmosphere-ocean interactions in supermodeling the tropical Pacific climate

NASA Astrophysics Data System (ADS)

Shen, Mao-Lin; Keenlyside, Noel; Bhatt, Bhuwan C.; Duane, Gregory S.

2017-12-01

The supermodel strategy interactively combines several models to outperform the individual models comprising it. A key advantage of the approach is that nonlinear improvements can be achieved, in contrast to the linear weighted combination of individual unconnected models. This property is found in a climate supermodel constructed by coupling two versions of an atmospheric model differing only in their convection scheme to a single ocean model. The ocean model receives a weighted combination of the momentum and heat fluxes. Optimal weights can produce a supermodel with a basic state similar to observations: a single Intertropical Convergence zone (ITCZ), with a western Pacific warm pool and an equatorial cold tongue. This is in stark contrast to the erroneous double ITCZ pattern simulated by both of the two stand-alone coupled models. By varying weights, we develop a conceptual scheme to explain how combining the momentum fluxes of the two different atmospheric models affects equatorial upwelling and surface wind feedback so as to give a realistic basic state in the tropical Pacific. In particular, we propose a mechanism based on the competing influences of equatorial zonal wind and off-equatorial wind stress curl in driving equatorial upwelling in the coupled models. Our results show how nonlinear ocean-atmosphere interaction is essential in combining these two effects to build different sea surface temperature structures, some of which are realistic. They also provide some insight into observed and modelled tropical Pacific climate.

Role of atmosphere-ocean interactions in supermodeling the tropical Pacific climate.

PubMed

Shen, Mao-Lin; Keenlyside, Noel; Bhatt, Bhuwan C; Duane, Gregory S

2017-12-01

The supermodel strategy interactively combines several models to outperform the individual models comprising it. A key advantage of the approach is that nonlinear improvements can be achieved, in contrast to the linear weighted combination of individual unconnected models. This property is found in a climate supermodel constructed by coupling two versions of an atmospheric model differing only in their convection scheme to a single ocean model. The ocean model receives a weighted combination of the momentum and heat fluxes. Optimal weights can produce a supermodel with a basic state similar to observations: a single Intertropical Convergence zone (ITCZ), with a western Pacific warm pool and an equatorial cold tongue. This is in stark contrast to the erroneous double ITCZ pattern simulated by both of the two stand-alone coupled models. By varying weights, we develop a conceptual scheme to explain how combining the momentum fluxes of the two different atmospheric models affects equatorial upwelling and surface wind feedback so as to give a realistic basic state in the tropical Pacific. In particular, we propose a mechanism based on the competing influences of equatorial zonal wind and off-equatorial wind stress curl in driving equatorial upwelling in the coupled models. Our results show how nonlinear ocean-atmosphere interaction is essential in combining these two effects to build different sea surface temperature structures, some of which are realistic. They also provide some insight into observed and modelled tropical Pacific climate.

Using altimetry to help explain patchy changes in hydrographic carbon measurements

NASA Astrophysics Data System (ADS)

Rodgers, Keith B.; Key, Robert M.; Gnanadesikan, Anand; Sarmiento, Jorge L.; Aumont, Olivier; Bopp, Laurent; Doney, Scott C.; Dunne, John P.; Glover, David M.; Ishida, Akio; Ishii, Masao; Jacobson, Andrew R.; Lo Monaco, Claire; Maier-Reimer, Ernst; Mercier, Herlé; Metzl, Nicolas; PéRez, Fiz F.; Rios, Aida F.; Wanninkhof, Rik; Wetzel, Patrick; Winn, Christopher D.; Yamanaka, Yasuhiro

2009-09-01

Here we use observations and ocean models to identify mechanisms driving large seasonal to interannual variations in dissolved inorganic carbon (DIC) and dissolved oxygen (O2) in the upper ocean. We begin with observations linking variations in upper ocean DIC and O2 inventories with changes in the physical state of the ocean. Models are subsequently used to address the extent to which the relationships derived from short-timescale (6 months to 2 years) repeat measurements are representative of variations over larger spatial and temporal scales. The main new result is that convergence and divergence (column stretching) attributed to baroclinic Rossby waves can make a first-order contribution to DIC and O2 variability in the upper ocean. This results in a close correspondence between natural variations in DIC and O2 column inventory variations and sea surface height (SSH) variations over much of the ocean. Oceanic Rossby wave activity is an intrinsic part of the natural variability in the climate system and is elevated even in the absence of significant interannual variability in climate mode indices. The close correspondence between SSH and both DIC and O2 column inventories for many regions suggests that SSH changes (inferred from satellite altimetry) may prove useful in reducing uncertainty in separating natural and anthropogenic DIC signals (using measurements from Climate Variability and Predictability's CO2/Repeat Hydrography program).

Energetics of global ocean tides from Geosat altimetry

NASA Technical Reports Server (NTRS)

Cartwright, David E.; Ray, Richard D.

1991-01-01

The present paper focuses on resonance and energetics of the daily tides, especially in the southern ocean, the distribution of gravitational power input of daily and half-daily tides, and comparison with other estimates of global dissipation rates. The present global tidal maps, derived from Geosat altimetry, compare favorably with ground truth data at about the same rms level as the models of Schwiderski (1983), and are slightly better in lunar than in solar tides. Diurnal admittances clearly show Kelvin wave structure in the southern ocean and confirm the resonant mode of Platzman (1984) at 28.5 + or - 0.1 hr with an apparent Q of about 4. Driving energy is found to enter dominantly in the North Pacific for the daily tides and is strongly peaked in the tropical oceans for the half-daily tides. Global rates of working on all major tide constituents except S2 agree well with independent results from analyses of gravity through satellite tracking. Comparison at S2 is improved by allowing for the air tide in gravitational results but suggests deficiencies in all solar tide models.

Oceanographic and atmospheric conditions on the continental shelf north of the Monterey Bay during August 2006

NASA Astrophysics Data System (ADS)

Ramp, Steven R.; Lermusiaux, Pierre F. J.; Shulman, Igor; Chao, Yi; Wolf, Rebecca E.; Bahr, Frederick L.

2011-09-01

A comprehensive data set from the ocean and atmosphere was obtained just north of the Monterey Bay as part of the Monterey Bay 2006 (MB06) field experiment. The wind stress, heat fluxes, and sea surface temperature were sampled by the Naval Postgraduate School's TWIN OTTER research aircraft. In situ data were collected using ships, moorings, gliders and AUVs. Four data-assimilating numerical models were additionally run, including the Coupled Ocean/Atmosphere Mesoscale Prediction System (COAMPS ®) model for the atmosphere and the Harvard Ocean Prediction System (HOPS), the Regional Ocean Modeling System (ROMS), and the Navy Coastal Ocean Model (NCOM) for the ocean. The scientific focus of the Adaptive Sampling and Prediction Experiment (ASAP) was on the upwelling/relaxation cycle and the resulting three-dimensional coastal circulation near a coastal promontory, in this case Point Año Nuevo, CA. The emphasis of this study is on the circulation over the continental shelf as estimated from the wind forcing, two ADCP moorings, and model outputs. The wind stress during August 2006 consisted of 3-10 day upwelling favorable events separated by brief 1-3 day relaxations. During the first two weeks there was some correlation between local winds and currents and the three models' capability to reproduce the events. During the last two weeks, largely equatorward surface wind stress forced the sea surface and barotropic poleward flow occurred over the shelf, reducing model skill at predicting the circulation. The poleward flow was apparently remotely forced by mesoscale eddies and alongshore pressure gradients, which were not well simulated by the models. The small, high-resolution model domains were highly reliant on correct open boundary conditions to drive these larger-scale poleward flows. Multiply-nested models were no more effective than well-initialized local models in this respect.

Plankton networks driving carbon export in the oligotrophic ocean

PubMed Central

Larhlimi, Abdelhalim; Roux, Simon; Darzi, Youssef; Audic, Stephane; Berline, Léo; Brum, Jennifer; Coelho, Luis Pedro; Espinoza, Julio Cesar Ignacio; Malviya, Shruti; Sunagawa, Shinichi; Dimier, Céline; Kandels-Lewis, Stefanie; Picheral, Marc; Poulain, Julie; Searson, Sarah; Stemmann, Lars; Not, Fabrice; Hingamp, Pascal; Speich, Sabrina; Follows, Mick; Karp-Boss, Lee; Boss, Emmanuel; Ogata, Hiroyuki; Pesant, Stephane; Weissenbach, Jean; Wincker, Patrick; Acinas, Silvia G.; Bork, Peer; de Vargas, Colomban; Iudicone, Daniele; Sullivan, Matthew B.; Raes, Jeroen; Karsenti, Eric; Bowler, Chris; Gorsky, Gabriel

2015-01-01

The biological carbon pump is the process by which CO2 is transformed to organic carbon via photosynthesis, exported through sinking particles, and finally sequestered in the deep ocean. While the intensity of the pump correlates with plankton community composition, the underlying ecosystem structure driving the process remains largely uncharacterised. Here we use environmental and metagenomic data gathered during the Tara Oceans expedition to improve our understanding of carbon export in the oligotrophic ocean. We show that specific plankton communities, from the surface and deep chlorophyll maximum, correlate with carbon export at 150 m and highlight unexpected taxa such as Radiolaria, alveolate parasites, as well as Synechococcus and their phages, as lineages most strongly associated with carbon export in the subtropical, nutrient-depleted, oligotrophic ocean. Additionally, we show that the relative abundance of just a few bacterial and viral genes can predict most of the variability in carbon export in these regions. PMID:26863193

Plankton networks driving carbon export in the oligotrophic ocean

NASA Astrophysics Data System (ADS)

2016-04-01

The biological carbon pump is the process by which CO2 is transformed to organic carbon via photosynthesis, exported through sinking particles, and finally sequestered in the deep ocean. While the intensity of the pump correlates with plankton community composition, the underlying ecosystem structure driving the process remains largely uncharacterized. Here we use environmental and metagenomic data gathered during the Tara Oceans expedition to improve our understanding of carbon export in the oligotrophic ocean. We show that specific plankton communities, from the surface and deep chlorophyll maximum, correlate with carbon export at 150 m and highlight unexpected taxa such as Radiolaria and alveolate parasites, as well as Synechococcus and their phages, as lineages most strongly associated with carbon export in the subtropical, nutrient-depleted, oligotrophic ocean. Additionally, we show that the relative abundance of a few bacterial and viral genes can predict a significant fraction of the variability in carbon export in these regions.

Optical Measurements and Modeling to Estimate Concentrations and Fluxes of Organic Matter in the Southern Ocean

NASA Technical Reports Server (NTRS)

Stramski, Dariusz; Mitchell, B. Greg; Marra, John W. (Technical Monitor)

2001-01-01

This project was a collaboration between two Principal Investigators, Dr. Dariusz Stramski and Dr. Greg Mitchell of Scripps Institution of Oceanography, University of California San Diego. Our overall goal was to conduct optical measurements and modeling to estimate concentrations of organic matter in the Southern Ocean in support of the U.S. JGOFS Process Study in this region. Key variables and processes of high relevance to accomplish the JGOFS goals include time and space resolution of phytoplankton pigments, particulate organic carbon, and the formation and export of organic carbon. Our project focused on establishing the fundamental relationships for parameterization of these variables and processes in terms of the optical properties of seawater, and developing understanding of why the Southern Ocean differs from other low-latitude systems, or has differentiation within. Our approach builds upon historical observations that optical properties provide a useful proxy for key reservoirs of organic matter such as chlorophyll alpha (Chl) and particulate organic carbon (POC) concentrations, which are of relevance to the JGOFS objectives. We carried out detailed studies of in situ and water sample optical properties including spectral reflectance, absorption, beam attenuation, scattering, and backscattering coefficients. We evaluated the ability to estimate Chl from the spectral reflectance (ocean color) in the Southern Ocean. We examined relationships between the ocean optical properties and particulate organic carbon. We developed, for the first time, an algorithm for estimating particulate organic carbon concentration in the surface ocean from satellite imagery of ocean color. With this algorithm, we obtained maps of POC distribution in the Southern Ocean showing the seasonal progression of POC in the austral spring-summer season. We also developed a semianalytical reflectance model for the investigated polar waters based on our field measurements of absorption and backscattering coefficients and Chl-dependent parameterizations of these coefficients. With this model, libraries of expected reflectance spectra for various chlorophyll concentrations can be generated with high spectral resolution for specific oceanic regions. In addition, our semianalytical reflectance model provided insight into the mechanisms which drive the empirical relationships between the ocean color and chlorophyll concentration. Our optical approach to the study of pigment and carbon concentrations will be directly relevant to development of system models and long-term monitoring of the Southern Ocean.

A new multi-proxy reconstruction of Atlantic deep ocean circulation during the warm mid-Pliocene

NASA Astrophysics Data System (ADS)

Riesselman, C. R.; Dowsett, H. J.; Scher, H. D.; Robinson, M. M.

2011-12-01

The mid-Pliocene (3.264 - 3.025 Ma) is the most recent interval in Earth's history with sustained global temperatures in the range of warming predicted for the 21st century, providing an appealing analog with which to examine the Earth system changes we might encounter in the coming century. Ongoing sea surface and deep ocean temperature reconstructions and coupled ocean-atmosphere general circulation model simulations by the USGS PRISM (Pliocene Research Interpretation and Synoptic Mapping) Group identify a dramatic North Atlantic warm anomaly coupled with increased evaporation in the mid-Pliocene, possibly driving enhanced meridional overturning circulation and North Atlantic Deep Water production. However deep ocean temperature is not a conclusive proxy for water mass, and most coupled model simulations predict transient decreases in North Atlantic Deep Water production in 21st century, presenting a contrasting picture of future warmer worlds. Here, we present early results from a new multi-proxy reconstruction of Atlantic deep ocean circulation during the warm mid-Pliocene, using δ13C of benthic foraminifera as a proxy for water mass age and the neodymium isotopic imprint on fossil fish teeth as a proxy for water mass source region along a three-site depth transect from the Walvis Ridge (subtropical South Atlantic). The deep ocean circulation reconstructions resulting from this project will add a new dimension to the PRISM effort and will be useful for both initialization and evaluation of future model simulations.

Beyond the bipolar seesaw: Toward a process understanding of interhemispheric coupling

NASA Astrophysics Data System (ADS)

Pedro, Joel B.; Jochum, Markus; Buizert, Christo; He, Feng; Barker, Stephen; Rasmussen, Sune O.

2018-07-01

The thermal bipolar ocean seesaw hypothesis was advanced by Stocker and Johnsen (2003) as the 'simplest possible thermodynamic model' to explain the time relationship between Dansgaard-Oeschger (DO) and Antarctic Isotope Maxima (AIM) events. In this review we combine palaeoclimate observations, theory and general circulation model experiments to advance from the conceptual model toward a process understanding of interhemispheric coupling and the forcing of AIM events. We present four main results: (1) Changes in Atlantic heat transport invoked by the thermal seesaw are partially compensated by opposing changes in heat transport by the global atmosphere and Pacific Ocean. This compensation is an integral part of interhemispheric coupling, with a major influence on the global pattern of climate anomalies. (2) We support the role of a heat reservoir in interhemispheric coupling but argue that its location is the global interior ocean to the north of the Antarctic Circumpolar Current (ACC), not the commonly assumed Southern Ocean. (3) Energy budget analysis indicates that the process driving Antarctic warming during AIM events is an increase in poleward atmospheric heat and moisture transport following sea ice retreat and surface warming over the Southern Ocean. (4) The Antarctic sea ice retreat is itself driven by eddy-heat fluxes across the ACC, amplified by sea-ice-albedo feedbacks. The lag of Antarctic warming after AMOC collapse reflects the time required for heat to accumulate in the ocean interior north of the ACC (predominantly the upper 1500 m), before it can be mixed across this dynamic barrier by eddies.

Remote SST Forcing and Local Land-Atmosphere Moisture Coupling as Drivers of Amazon Temperature and Carbon Cycle Variability

NASA Astrophysics Data System (ADS)

Levine, P. A.; Xu, M.; Chen, Y.; Randerson, J. T.; Hoffman, F. M.

2017-12-01

Interannual variability of climatic conditions in the Amazon rainforest is associated with El Niño-Southern Oscillation (ENSO) and ocean-atmosphere interactions in the North Atlantic. Sea surface temperature (SST) anomalies in these remote ocean regions drive teleconnections with Amazonian surface air temperature (T), precipitation (P), and net ecosystem production (NEP). While SST-driven NEP anomalies have been primarily linked to T anomalies, it is unclear how much the T anomalies result directly from SST forcing of atmospheric circulation, and how much result indirectly from decreases in precipitation that, in turn, influence surface energy fluxes. Interannual variability of P associated with SST anomalies lead to variability in soil moisture (SM), which would indirectly affect T via partitioning of turbulent heat fluxes between the land surface and the atmosphere. To separate the direct and indirect influence of the SST signal on T and NEP, we performed a mechanism-denial experiment to decouple SST and SM anomalies. We used the Accelerated Climate Modeling for Energy (ACMEv0.3), with version 5 of the Community Atmosphere Model and version 4.5 of the Community Land Model. We forced the model with observed SSTs from 1982-2016. We found that SST and SM variability both contribute to T and NEP anomalies in the Amazon, with relative contributions depending on lag time and location within the Amazon basin. SST anomalies associated with ENSO drive most of the T variability at shorter lag times, while the ENSO-driven SM anomalies contribute more to T variability at longer lag times. SM variability and the resulting influence on T anomalies are much stronger in the eastern Amazon than in the west. Comparing modeled T with observations demonstrate that SST alone is sufficient for simulating the correct timing of T variability, but SM anomalies are necessary for simulating the correct magnitude of the T variability. Modeled NEP indicated that variability in carbon fluxes results from both SST and SM anomalies. As with T, SM anomalies affect NEP at a much longer lag time than SST anomalies. These results highlight the role of land-atmosphere coupling in driving climate variability within the Amazon, and suggest that land atmospheric coupling may amplify and delay carbon cycle responses to ocean-atmosphere teleconnections.

Plate motion changes drive Eastern Indian Ocean microcontinent formation

NASA Astrophysics Data System (ADS)

Whittaker, J. M.; Williams, S.; Halpin, J.; Wild, T.; Stilwell, J.; Jourdan, F.; Daczko, N. R.

2016-12-01

The roles of plate tectonic or mantle dynamic forces in rupturing continental lithosphere remain controversial. Particularly enigmatic is the rifting of microcontinents from mature continental rifted margin - several well-studied microcontinent calving events coincide in space and time with mantle plume activity, but the significance of plumes in driving microcontinent formation remains controversial, and a role for plate-driven processes has also been suggested. In 2011, our team discovered two new microcontinents in the eastern Indian Ocean, the Batavia and Gulden Draak microcontinents. These microcontinents are unique as they are the only surviving remnants of the now-destroyed or highly deformed Greater Indian margin and provide us with an opportunity to test existing models of microcontinent formation against new observations. Here, we explore models for microcontinent formation using our new data from the Eastern Indian Ocean in a plate tectonic reconstruction framework. We use Argon dating and paleontology results to constrain calving from greater India at 101-104 Ma. This region had been proximal to the active Kerguelen plume for 30 Myrs but we demonstrate that calving did not correspond with a burst of volcanic activity. Rather, it is likely that plume-related thermal weakening of the Indian passive margin preconditioned it for microcontinent formation but calving was triggered by changes in plate tectonic boundary forces. Changes in the relative motions between Indian and Australia led to increasing compressive forces along the long-offset Wallaby-Zenith Fracture Zone, which was eventually abandoned during the jump of the spreading ridge into the Indian continental margin.

Spreading continents kick-started plate tectonics.

PubMed

Rey, Patrice F; Coltice, Nicolas; Flament, Nicolas

2014-09-18

Stresses acting on cold, thick and negatively buoyant oceanic lithosphere are thought to be crucial to the initiation of subduction and the operation of plate tectonics, which characterizes the present-day geodynamics of the Earth. Because the Earth's interior was hotter in the Archaean eon, the oceanic crust may have been thicker, thereby making the oceanic lithosphere more buoyant than at present, and whether subduction and plate tectonics occurred during this time is ambiguous, both in the geological record and in geodynamic models. Here we show that because the oceanic crust was thick and buoyant, early continents may have produced intra-lithospheric gravitational stresses large enough to drive their gravitational spreading, to initiate subduction at their margins and to trigger episodes of subduction. Our model predicts the co-occurrence of deep to progressively shallower mafic volcanics and arc magmatism within continents in a self-consistent geodynamic framework, explaining the enigmatic multimodal volcanism and tectonic record of Archaean cratons. Moreover, our model predicts a petrological stratification and tectonic structure of the sub-continental lithospheric mantle, two predictions that are consistent with xenolith and seismic studies, respectively, and consistent with the existence of a mid-lithospheric seismic discontinuity. The slow gravitational collapse of early continents could have kick-started transient episodes of plate tectonics until, as the Earth's interior cooled and oceanic lithosphere became heavier, plate tectonics became self-sustaining.

Causes of the large warm bias in the Angola-Benguela Frontal Zone in the Norwegian Earth System Model

NASA Astrophysics Data System (ADS)

Koseki, Shunya; Keenlyside, Noel; Demissie, Teferi; Toniazzo, Thomas; Counillon, Francois; Bethke, Ingo; Ilicak, Mehmet; Shen, Mao-Lin

2018-06-01

We have investigated the causes of the sea surface temperature (SST) bias in the Angola-Benguela Frontal Zone (ABFZ) of the southeastern Atlantic Ocean simulated by the Norwegian Earth System Model (NorESM). Similar to other coupled-models, NorESM has a warm SST bias in the ABFZ of up to 8 °C in the annual mean. Our analysis of NorESM reveals that a cyclonic surface wind bias over the ABFZ drives a locally excessively strong southward (0.05 m/s (relative to observation)) Angola Current displacing the ABFZ southward. A series of uncoupled stand-alone atmosphere and ocean model simulations are performed to investigate the cause of the coupled model bias. The stand-alone atmosphere model driven with observed SST exhibits a similar cyclonic surface circulation bias; while the stand-alone ocean model forced with the reanalysis data produces a warm SST in the ABFZ with a magnitude approximately half of that in the coupled NorESM simulation. An additional uncoupled sensitivity experiment shows that the atmospheric model's local negative surface wind curl generates anomalously strong Angola Current at the ocean surface. Consequently, this contributes to the warm SST bias in the ABFZ by 2 °C (compared to the reanalysis forced simulation). There is no evidence that local air-sea feedbacks among wind stress curl, SST, and sea level pressure (SLP) affect the ABFZ SST bias. Turbulent surface heat flux differences between coupled and uncoupled experiments explain the remaining 2 °C warm SST bias in NorESM. Ocean circulation, upwelling and turbulent heat flux errors all modulate the intensity and the seasonality of the ABFZ errors.

Modeling coral calcification accounting for the impacts of coral bleaching and ocean acidification

NASA Astrophysics Data System (ADS)

Evenhuis, C.; Lenton, A.; Cantin, N. E.; Lough, J. M.

2014-01-01

Coral reefs are diverse ecosystems threatened by rising CO2 levels that are driving the observed increases in sea surface temperature and ocean acidification. Here we present a new unified model that links changes in temperature and carbonate chemistry to coral health. Changes in coral health and population are able to explicitly modelled by linking the rates of growth, recovery and calcification to the rates of bleaching and temperature stress induced mortality. The model is underpinned by four key principles: the Arrhenius equation, thermal specialisation, resource allocation trade-offs, and adaption to local environments. These general relationships allow this model to be constructed from a range of experimental and observational data. The different characteristics of this model are also assessed against independent data to show that the model captures the observed response of corals. We also provide new insights into the factors that determine calcification rates and provide a framework based on well-known biological principles for understanding the observed global distribution of calcification rates. Our results suggest that, despite the implicit complexity of the coral reef environment, a simple model based on temperature, carbonate chemistry and different species can reproduce much of the observed response of corals to changes in temperature and ocean acidification.

A Unified Model for Methylmercury Formation and Bioaccumulation in the Global Ocean

NASA Astrophysics Data System (ADS)

Zhang, Y.; Schartup, A. T.; Soerensen, A.; Dutkiewicz, S.; Sunderland, E. M.

2017-12-01

Marine fish consumption is the main exposure pathway for methylmercury (MeHg), a neurotoxin, in many countries. The Hg in the ocean is mainly from atmospheric deposition in inorganic forms. How the deposited Hg is methylated and accumulated in biota remain an open question. We develop a 3D model (MITgcm) for MeHg formation and bioaccumulation in the global ocean and evaluate the driving factors. The model is based on a previous published inorganic Hg model and is coupled with the bioaccumulation model for marine methylmercury (BAM3) with ocean biogeochemistry from DARWIN model. We develop a unified scheme that scales methylation by microbe activity and assumes demethylation a function of short wave radiation and temperature. The model result agrees well with currently available observations at the 0-100 m (mod.: 43±52 fM vs obs.: 69±67 fM, 1 fM = 10-15 mol/L), 500 m (360±280 fM vs 340±260 fM), and 1000 m depth (260±170 fM vs 290±210 fM). In the surface ocean, we find the MeHg concentrations are a function of latitude, resulting from photodemethylation. The model reproduces the high concentrations observed over the sub-thermocline of Pacific Subarctic Gyre, which is associated with active microbe activity. On the other hand, both the model and observations suggest low concentrations over oligotrophic regions such as Indian Ocean Gyre. In the tropical oceans, the model predicts the highest MeHg concentrations, consistent with observation, and it is caused by the overlapping high atmospheric deposition and active microbe activities. The model captures the high concentrations in the subsurface of the Arctic and Southern Ocean where low temperature slows down abiotic demethylation. The modeled global average MeHg concentration in phytoplankton is 2.0 ng/g (by wet weight), within the same range of observations. High concentrations are modeled over tropical and high-latitude regions due to the dominance of small sized prochlorococcus and high seawater concentrations, respectively. Due to the different palatability of phytoplankton to zooplankton, the small zooplankton has 96% of MeHg grazed from picoplankton, but the large zooplankton mainly from microplankton (92%). The MeHg concentrations are higher in large zooplankton (9.3 ng/g) than small ones (2.6 ng/g) with spatial patterns influenced by their main food sources.

Understanding multidecadal variability in ENSO amplitude

NASA Astrophysics Data System (ADS)

Russell, A.; Gnanadesikan, A.

2013-12-01

Sea surface temperatures (SSTs) in the tropical Pacific vary as a result of the coupling between the ocean and atmosphere driven largely by the El Niño - Southern Oscillation (ENSO). ENSO has a large impact on the local climate and hydrology of the tropical Pacific, as well as broad-reaching effects on global climate. ENSO amplitude is known to vary on long timescales, which makes it very difficult to quantify its response to climate change and constrain the physical processes that drive it. In order to assess the extent of unforced multidecadal changes in ENSO variability, a linear regression of local SST changes is applied to the GFDL CM2.1 model 4000-yr pre-industrial control run. The resulting regression coefficient strengths, which represent the sensitivity of SST changes to thermocline depth and zonal wind stress, vary by up to a factor of 2 on multi-decadal time scales. This long-term modulation in ocean-atmosphere coupling is highly correlated with ENSO variability, but do not explain the reasons for such variability. Variation in the relationship between SST changes and wind stress points to a role for changing stratification in the central equatorial Pacific in modulating ENSO amplitudes with stronger stratification reducing the response to winds. The main driving mechanism we have identified for higher ENSO variance are changes in the response of zonal winds to SST anomalies. The shifting convection and precipitation patterns associated with the changing state of the atmosphere also contribute to the variability of the regression coefficients. These mechanisms drive much of the variability in ENSO amplitude and hence ocean-atmosphere coupling in the tropical Pacific.

Connecting the dots in the Gulf of the Farallones: linking physical ocean conditions and nutrients to the ecological success of planktivorous predators

NASA Astrophysics Data System (ADS)

Hartnett, R. J.; Jahncke, J.; Wilkerson, F. P.; Nielsen, K. J.; Nur, N.

2016-02-01

Nutrients are essential for phytoplankton to thrive and drive bottom-up forcing of ecosystem production. Upwelling of deep water from the shelf break delivers pulses of nutrients resulting in recurring blooms of phytoplankton and zooplankton in the Gulf of the Farallones (GoF) region of the California Current Ecosystem, supporting a diversity of pelagic predators. Anomalies in ocean conditions are often associated with booms and crashes of these predator populations, such as the recent mortality of thousands of Cassin's Auklets. These anomalies are often associated with changes in physical conditions affecting the Pacific Ocean, as well as more localized physical conditions along the California coastline that drive nutrient availability, but the specific role of nutrients in driving the abundances of top predators has not been directly examined. Using a ten-year multivariate time series from the GoF, including nutrient concentrations, we test the hypothesis that nutrients regulate the abundance of plankton and planktivorous predators, as a result of physical forcing. Using path analysis we test alternate interaction webs, including the direct and indirect effects of physical and biological factors on pelagic predator abundances. Insights from this work may be useful to marine resource managers in understanding how future variability in ocean conditions may drive ecosystem conditions including the abundance of pelagic predators in the GoF Marine Sanctuary.

Disentangling the Roles of Atmospheric and Oceanic Forcing on the Last Deglaciation of the Greenland Ice Sheet

NASA Astrophysics Data System (ADS)

Keisling, B. A.; Deconto, R. M.

2017-12-01

Today the Greenland Ice Sheet loses mass via both oceanic and atmospheric processes. However, the relative importance of these mass balance components is debated, especially their potential impact on ongoing and future mass imbalance. Discerning the impact of oceanic versus atmospheric forcing during past periods of mass loss provides potential insight into the future behavior of the ice sheet. Here we present an ensemble of Greenland Ice Sheet simulations of the last deglaciation, designed to assess separately the roles of the ocean and the atmosphere in driving mass loss over the last twenty thousand years. We use twenty-eight different ocean forcing scenarios along with a cutting-edge reconstruction of time-evolving atmospheric conditions based on climate model output and δ15N-based temperature reconstructions to generate a range of ice-sheet responses during the deglaciation. We then compare the simulated timing of ice-retreat in individual catchments with estimates based on both 10Be (exposure) and 14C (minimum-limiting) dates. These experiments allow us to identify the ocean forcing scenario that best match the data on a local-to-regional (i.e., 100-1000 km) scales, providing an assessment of the relative importance of ocean and atmospheric forcing components around the periphery of Greenland. We use these simulations to quantify the importance of the three major mass balance terms (calving, oceanic melting, and surface melting) and assess the uncertainty of the relative influence of these factors during the most recent periods of major ice loss. Our results show that mass balance components around different sectors of the ice sheet respond differently to forcing, with oceanic components driving the majority of retreat in south and east Greenland and atmospheric forcing dominating in west and north Greenland In addition, we target three areas at high spatial resolution ( 1 km) around Greenland currently undergoing substantial change (Jakobshavn, Petermann, and Nioghalvfjerdsfjord/Zakariae) to directly compare simulated deglacial retreat rates with those implied by submarine and subaerial moraine systems.

Molybdenum isotope behaviour in groundwaters and terrestrial hydrothermal systems, Iceland

NASA Astrophysics Data System (ADS)

Neely, Rebecca A.; Gislason, Sigurdur R.; Ólafsson, Magnus; McCoy-West, Alex J.; Pearce, Christopher R.; Burton, Kevin W.

2018-03-01

Molybdenum (Mo) isotopes have proved useful in the reconstruction of paleoredox conditions. Their application generally relies upon a simplified model of ocean inputs in which rivers dominate Mo fluxes to the oceans and hydrothermal fluids are considered to be a minor contribution. To date, however, little attention has been paid to the extent of Mo isotope variation of hydrothermal waters, or to the potential effect of direct groundwater discharge to the oceans. Here we present Mo isotope data for two Icelandic groundwater systems (Mývatn and Þeistareykir) that are both influenced by hydrothermal processes. Relative to NIST 3134 = +0.25‰, the cold (<10 °C) groundwaters (δ98/95MoGROUNDWATER = -0.15‰ to +0.47‰; n = 13) show little, if any, fractionation from the host basalt (δ 98 / 95MoBASALT = +0.16‰ to -0.12‰) and are, on average, lighter than both global and Icelandic rivers. In contrast, waters that are hydrothermally influenced (>10 °C) possess isotopically heavy δ98/95MoHYDROTHERMAL values of +0.25‰ to +2.06‰ (n = 18) with the possibility that the high temperature endmembers are even heavier. Although the mechanisms driving this fractionation remain unresolved, the incongruent dissolution of the host basalt and both the dissolution and precipitation of sulfides are considered. Regardless of the processes driving these variations, the δ98Mo data presented in this study indicate that groundwater and hydrothermal waters have the potential to modify ocean budget calculations.

The Impact of the Assimilation of Aquarius Sea Surface Salinity Data in the GEOS Ocean Data Assimilation System

NASA Technical Reports Server (NTRS)

Vernieres, Guillaume Rene Jean; Kovach, Robin M.; Keppenne, Christian L.; Akella, Santharam; Brucker, Ludovic; Dinnat, Emmanuel Phillippe

2014-01-01

Ocean salinity and temperature differences drive thermohaline circulations. These properties also play a key role in the ocean-atmosphere coupling. With the availability of L-band space-borne observations, it becomes possible to provide global scale sea surface salinity (SSS) distribution. This study analyzes globally the along-track (Level 2) Aquarius SSS retrievals obtained using both passive and active L-band observations. Aquarius alongtrack retrieved SSS are assimilated into the ocean data assimilation component of Version 5 of the Goddard Earth Observing System (GEOS-5) assimilation and forecast model. We present a methodology to correct the large biases and errors apparent in Version 2.0 of the Aquarius SSS retrieval algorithm and map the observed Aquarius SSS retrieval into the ocean models bulk salinity in the topmost layer. The impact of the assimilation of the corrected SSS on the salinity analysis is evaluated by comparisons with insitu salinity observations from Argo. The results show a significant reduction of the global biases and RMS of observations-minus-forecast differences at in-situ locations. The most striking results are found in the tropics and southern latitudes. Our results highlight the complementary role and problems that arise during the assimilation of salinity information from in-situ (Argo) and space-borne surface (SSS) observations

75 FR 52343 - Ocean Transportation Intermediary License Applicants

Federal Register 2010, 2011, 2012, 2013, 2014

2010-08-25

... Company, Inc. (NVO & OFF), 4529 Angeles Crest Highway, Suite 300, La Canada, CA 91011, Officers: Ernest V..., Application Type: QI Change. BestOcean Worldwide Logistics, Inc. (OFF & NVO), 1300 Valley Vista Drive, Suite...

Oceanic response to buoyancy, wind and tidal forcing in a Greenlandic glacial fjord

NASA Astrophysics Data System (ADS)

Carroll, D.; Sutherland, D.; Shroyer, E.; Nash, J. D.

2013-12-01

The Greenland Ice Sheet is losing mass at an accelerating rate. This acceleration may in part be due to changes in oceanic heat transport to marine-terminating outlet glaciers. Ocean heat transport to glaciers depends upon fjord dynamics, which include buoyancy-driven estuarine exchange flow, tides, internal waves, turbulent mixing, and connections to the continental shelf. A 3D model of Rink Isbrae fjord in West Greenland is used to investigate the role of ocean forcing on heat transport to the glacier face. Initial conditions are prescribed from oceanographic field data collected in Summer 2013; wind and tidal forcing, along with meltwater flux, are varied in individual model runs. Subglacial meltwater flux values range from 25-500 m3 s-1. For low discharge values, a subsurface plume drives circulation in the fjord. Our simulations indicate that offshore wind forcing is the dominant mechanism for exchange flow between the fjord and the continental shelf. These results show that glacial fjord circulation is a complex, 3D process with multi-cell estuarine circulation and large velocity shears due to coastal winds. Our results are a first step towards a realistic 3D representation of a high-latitude glacial fjord in a numerical model, and will provide insight to future observational studies.

Marine biogeochemical influence on primary sea spray aerosol composition in the Southern Ocean: predictions from a mechanistic model

NASA Astrophysics Data System (ADS)

McCoy, D.; Burrows, S. M.; Elliott, S.; Frossard, A. A.; Russell, L. M.; Liu, X.; Ogunro, O. O.; Easter, R. C.; Rasch, P. J.

2014-12-01

Remote marine clouds, such as those over the Southern Ocean, are particularly sensitive to variations in the concentration and chemical composition of aerosols that serve as cloud condensation nuclei (CCN). Observational evidence indicates that the organic content of fine marine aerosol is greatly increased during the biologically active season near strong phytoplankton blooms in certain locations, while being nearly constant in other locations. We have recently developed a novel modeling framework that mechanistically links the organic fraction of submicron sea spray to ocean biogeochemistry (Burrows et al., in discussion, ACPD, 2014; Elliott et al., ERL, 2014). Because of its combination of large phytoplankton blooms and high wind speeds, the Southern Ocean is an ideal location for testing our understanding of the processes driving the enrichment of organics in sea spray aerosol. Comparison of the simulated OM fraction with satellite observations shows that OM fraction is a statistically significant predictor of cloud droplet number concentration over the Southern Ocean. This presentation will focus on predictions from our modeling framework for the Southern Ocean, specifically, the predicted geographic gradients and seasonal cycles in the aerosol organic matter and its functional group composition. The timing and location of a Southern Ocean field campaign will determine its utility in observing the effects of highly localized and seasonal phytoplankton blooms on aerosol composition and clouds. Reference cited: Burrows, S. M., Ogunro, O., Frossard, A. A., Russell, L. M., Rasch, P. J., and Elliott, S.: A physically-based framework for modelling the organic fractionation of sea spray aerosol from bubble film Langmuir equilibria, Atmos. Chem. Phys. Discuss., 14, 5375-5443, doi:10.5194/acpd-14-5375-2014, 2014. Elliott, S., Burrows, S. M., Deal, C., Liu, X., Long, M., Ogunro, O., Russell, L. M., and Wingenter O.. "Prospects for simulating macromolecular surfactant chemistry at the ocean-atmosphere boundary." Environmental Research Letters 9, no. 6 (2014): 064012.

Design of the MISMIP+, ISOMIP+, and MISOMIP ice-sheet, ocean, and coupled ice sheet-ocean intercomparison projects

NASA Astrophysics Data System (ADS)

Asay-Davis, Xylar; Cornford, Stephen; Martin, Daniel; Gudmundsson, Hilmar; Holland, David; Holland, Denise

2015-04-01

The MISMIP and MISMIP3D marine ice sheet model intercomparison exercises have become popular benchmarks, and several modeling groups have used them to show how their models compare to both analytical results and other models. Similarly, the ISOMIP (Ice Shelf-Ocean Model Intercomparison Project) experiments have acted as a proving ground for ocean models with sub-ice-shelf cavities.As coupled ice sheet-ocean models become available, an updated set of benchmark experiments is needed. To this end, we propose sequel experiments, MISMIP+ and ISOMIP+, with an end goal of coupling the two in a third intercomparison exercise, MISOMIP (the Marine Ice Sheet-Ocean Model Intercomparison Project). Like MISMIP3D, the MISMIP+ experiments take place in an idealized, three-dimensional setting and compare full 3D (Stokes) and reduced, hydrostatic models. Unlike the earlier exercises, the primary focus will be the response of models to sub-shelf melting. The chosen configuration features an ice shelf that experiences substantial lateral shear and buttresses the upstream ice, and so is well suited to melting experiments. Differences between the steady states of each model are minor compared to the response to melt-rate perturbations, reflecting typical real-world applications where parameters are chosen so that the initial states of all models tend to match observations. The three ISOMIP+ experiments have been designed to to make use of the same bedrock topography as MISMIP+ and using ice-shelf geometries from MISMIP+ results produced by the BISICLES ice-sheet model. The first two experiments use static ice-shelf geometries to simulate the evolution of ocean dynamics and resulting melt rates to a quasi-steady state when far-field forcing changes in either from cold to warm or from warm to cold states. The third experiment prescribes 200 years of dynamic ice-shelf geometry (with both retreating and advancing ice) based on a BISICLES simulation along with similar flips between warm and cold states in the far-field ocean forcing. The MISOMIP experiment combines the MISMIP+ experiments with the third ISOMIP+ experiment. Changes in far-field ocean forcing lead to a rapid (over ~1-2 years) increase in sub-ice-shelf melting, which is allowed to drive ice-shelf retreat for ~100 years. Then, the far-field forcing is switched to a cold state, leading to a rapid decrease in melting and a subsequent advance over ~100 years. To illustrate, we present results from BISICLES and POP2x experiments for each of the three intercomparison exercises.

Development and applications of a Coupled-Ocean-Atmosphere-Wave-Sediment Transport (COAWST) Modeling System

NASA Astrophysics Data System (ADS)

Warner, J. C.; Armstrong, B. N.; He, R.; Zambon, J. B.; Olabarrieta, M.; Voulgaris, G.; Kumar, N.; Haas, K. A.

2012-12-01

Understanding processes responsible for coastal change is important for managing both our natural and economic coastal resources. Coastal processes respond from both local scale and larger regional scale forcings. Understanding these processes can lead to significant insight into how the coastal zone evolves. Storms are one of the primary driving forces causing coastal change from a coupling of wave and wind driven flows. Here we utilize a numerical modeling approach to investigate these dynamics of coastal storm impacts. We use the Coupled Ocean - Atmosphere - Wave - Sediment Transport (COAWST) Modeling System that utilizes the Model Coupling Toolkit to exchange prognostic variables between the ocean model ROMS, atmosphere model WRF, wave model SWAN, and the Community Sediment Transport Modeling System (CSTMS) sediment routines. The models exchange fields of sea-surface temperature, ocean currents, water levels, bathymetry, wave heights, lengths, periods, bottom orbital velocities, and atmospheric surface heat and momentum fluxes, atmospheric pressure, precipitation, and evaporation. Data fields are exchanged using regridded flux conservative sparse matrix interpolation weights computed from the SCRIP spherical coordinate remapping interpolation package. We describe the modeling components and the model field exchange methods. As part of the system, the wave and ocean models run with cascading, refined, spatial grids to provide increased resolution, scaling down to resolve nearshore wave driven flows simulated by the vortex force formulation, all within selected regions of a larger, coarser-scale coastal modeling system. The ocean and wave models are driven by the atmospheric component, which is affected by wave dependent ocean-surface roughness and sea surface temperature which modify the heat and momentum fluxes at the ocean-atmosphere interface. We describe the application of the modeling system to several regions of multi-scale complexity to identify the significance of larger scale forcing cascading down to smaller scales and to investigate the interactions of the coupled system with increasing degree of model-model interactions. Three examples include the impact of Hurricane Ivan in 2004 in the Gulf of Mexico, Hurricane Ida in 2009 that evolved into a tropical storm on the US East coast, and passage of strong cold fronts across the US southeast. Results identify that hurricane intensity is extremely sensitive to sea-surface temperature, with a reduction in intensity when the atmosphere is coupled to the ocean model due to rapid cooling of the ocean from the surface through the mixed layer. Coupling of the ocean to the atmosphere also results in decreased boundary layer stress and coupling of the waves to the atmosphere results in increased sea-surface stress. Wave results are sensitive to both ocean and atmospheric coupling due to wave-current interactions with the ocean and wave-growth from the atmospheric wind stress. Sediment resuspension at regional scale during the hurricane is controlled by shelf width and wave propagation during hurricane approach. Results from simulation of passage of cold fronts suggest that synoptic meteorological systems can strongly impact surf zone and inner shelf response, therefore act as a strong driver for long term littoral sediment transport. We will also present some of the challenges faced to develop the modeling system.

A perspective on the future of physical oceanography.

PubMed

Garabato, Alberto C Naveira

2012-12-13

The ocean flows because it is forced by winds, tides and exchanges of heat and freshwater with the overlying atmosphere and cryosphere. To achieve a state where the defining properties of the ocean (such as its energy and momentum) do not continuously increase, some form of dissipation or damping is required to balance the forcing. The ocean circulation is thought to be forced primarily at the large scales characteristic of ocean basins, yet to be damped at much smaller scales down to those of centimetre-sized turbulence. For decades, physical oceanographers have sought to comprehend the fundamentals of this fractal puzzle: how the ocean circulation is driven, how it is damped and how ocean dynamics connects the very different scales of forcing and dissipation. While in the last two decades significant advances have taken place on all these three fronts, the thrust of progress has been in understanding the driving mechanisms of ocean circulation and the ocean's ensuing dynamical response, with issues surrounding dissipation receiving comparatively little attention. This choice of research priorities stems not only from logistical and technological difficulties in observing and modelling the physical processes responsible for damping the circulation, but also from the untested assumption that the evolution of the ocean's state over time scales of concern to humankind is largely independent of dissipative processes. In this article, I illustrate some of the key advances in our understanding of ocean circulation that have been achieved in the last 20 years and, based on a range of evidence, contend that the field will soon reach a stage in which uncertainties surrounding the arrest of ocean circulation will pose the main challenge to further progress. It is argued that the role of the circulation in the coupled climate system will stand as a further focal point of major advances in understanding within the next two decades, supported by the drive of physical oceanography towards a more operational enterprise by contextual factors. The basic elements that a strategy for the future must have to foster progress in these two areas are discussed, with an overarching emphasis on the promotion of curiosity-driven fundamental research against opposing external pressures and on the importance of upholding fundamental research as the apex of education in the field.

Variations in freshwater pathways from the Arctic Ocean into the North Atlantic Ocean

NASA Astrophysics Data System (ADS)

Wang, Zeliang; Hamilton, James; Su, Jie

2017-06-01

Understanding the mechanisms that drive exchanges between the Arctic Ocean and adjacent oceans is critical to building our knowledge of how the Arctic is reacting to a warming climate, and how potential changes in Arctic Ocean freshwater export may impact the AMOC (Atlantic Meridional Overturning Circulation). Here, freshwater pathways from the Arctic Ocean to the North Atlantic are investigated using a 1 degree global model. An EOF analysis of modeled sea surface height (SSH) demonstrates that while the second mode accounts for only 15% of the variability, the associated geostrophic currents are strongly correlated with freshwater exports through CAA (Canadian Arctic Archipelago; r = 0.75), Nares Strait (r = 0.77) and Fram Strait (r = -0.60). Separation of sea level into contributing parts allows us to show that the EOF1 is primarily a barotropic mode reflecting variability in bottom pressure equivalent sea level, while the EOF2 mode reflects changes in steric height in the Arctic Basin. This second mode is linked to momentum wind driven surface current, and dominates the Arctic Ocean freshwater exports. Both the Arctic Oscillation and Arctic Dipole atmospheric indices are shown to be linked to Arctic Ocean freshwater exports, with the forcing associated with the Arctic Dipole reflecting the out-of-phase relationship between transports through the CAA and those through Fram Strait. Finally, observed freshwater transport variation through the CAA is found to be strongly correlated with tide gauge data from the Beaufort Sea coast (r = 0.81), and with the EOF2 mode of GRACE bottom pressure data (r = 0.85) on inter-annual timescales.

Comparing models of seasonal deformation to horizontal and vertical PBO GPS data

NASA Astrophysics Data System (ADS)

Bartlow, N. M.; Fialko, Y. A.; van Dam, T. M.

2015-12-01

GPS monuments around the world exhibit seasonal displacements in both the horizontal and vertical direction with amplitudes on the order of centimeters. For analysis of tectonic signals, researchers typically fit and remove a sine function with an annual period, and sometimes an additional sine function with a semiannual period. As interest grows in analyzing small-amplitude, long-period deformation signals it becomes more important to accurately correct for seasonal variations. It is well established that the vertical component of seasonal GPS signals is largely due to continental water storage cycles (e.g. van Dam et al., GRL, 2001). Other recognized sources of seasonal loading include atmospheric pressure loading and oceanic loading due to non-steric changes in ocean height (e.g. van Dam et al., J. Geodesy, 2012). Here we attempt to build a complete physical model of seasonal loading by considering all of these sources (continental water storage, atmospheric pressure, and oceanic loading) and comparing our model to horizontal and vertical GPS data in the Western US. Atmospheric loading effects are computed from the National Center for Environmental Prediction 6-hourly global reanalysis surface pressure fields; the terrestrial water loading and ocean loading models are generated using SPOTL (Some Programs for Ocean Tide Loading; Agnew, SIO Technical Report, 2012) and parameters from NASA's Land Data Assimilation Systems and the Estimating the Circulation and Climate of the Ocean model, version 4. We find that with a few exceptions, our seasonal loading model predicts the correct phases but underestimates the amplitudes of vertical seasonal loads, and is a generally poor fit to the observed horizontal seasonal signals. This implies that our understanding of the driving mechanisms behind seasonal variations in the GPS data is still incomplete and needs to be improved before physics-based models can be used as an effective correction tool for the GPS timeseries.

Relative influence of precession and obliquity in the early Holocene: Topographic modulation of subtropical seasonality during the Asian summer monsoon

NASA Astrophysics Data System (ADS)

Wu, Chi-Hua; Lee, Shih-Yu; Chiang, John C. H.

2018-07-01

On orbital timescales, higher summer insolation is thought to strengthen the continental monsoon while weakening the maritime monsoon in the Northern hemisphere. Through simulations using the Community Earth System Model, we evaluated the relative influence of perihelion precession and high obliquity in the early Holocene during the Asian summer monsoon. The major finding was that precession dominates the atmospheric heating change over the Tibetan Plateau-Himalayas and Maritime Continent, whereas obliquity is responsible for the heating change over the equatorial Indian Ocean. Thus, precession and obliquity can play contrasting roles in driving the monsoons on orbital timescales. In late spring-early summer, interior Asian continental heating drives the South and East Asian monsoons. The broad-scale monsoonal circulation further expands zonally in July-August, corresponding to the development of summer monsoons in West Africa and the subtropical Western North Pacific (WNP) as well as a sizable increase in convection over the equatorial Indian Ocean. Tropical and oceanic heating becomes crucial in late summer. Over South Asia-Indian Ocean (50°E-110°E), the precession maximum intensifies the monsoonal Hadley cell (heating with an inland/highland origin), which is opposite to the meridional circulation change induced by high obliquity (heating with a tropical origin). The existence of the Tibetan Plateau-Himalayas intensifies the precessional impact. During the late-summer phase of the monsoon season, the effect of obliquity on tropical heating can be substantial. In addition to competing with Asian continental heating, obliquity-enhanced heating over the equatorial Indian Ocean also has a Walker-type circulation impact, resulting in suppression of precession-enhanced heating over the Maritime Continent.

Dynamical downscaling of historical climate over CORDEX East Asia domain: A comparison of regional ocean-atmosphere coupled model to stand-alone RCM simulations

NASA Astrophysics Data System (ADS)

Zou, Liwei; Zhou, Tianjun; Peng, Dongdong

2016-02-01

The FROALS (flexible regional ocean-atmosphere-land system) model, a regional ocean-atmosphere coupled model, has been applied to the Coordinated Regional Downscaling Experiment (CORDEX) East Asia domain. Driven by historical simulations from a global climate system model, dynamical downscaling for the period from 1980 to 2005 has been conducted at a uniform horizontal resolution of 50 km. The impacts of regional air-sea couplings on the simulations of East Asian summer monsoon rainfall have been investigated, and comparisons have been made to corresponding simulations performed using a stand-alone regional climate model (RCM). The added value of the FROALS model with respect to the driving global climate model was evident in terms of both climatology and the interannual variability of summer rainfall over East China by the contributions of both the high horizontal resolution and the reasonably simulated convergence of the moisture fluxes. Compared with the stand-alone RCM simulations, the spatial pattern of the simulated low-level monsoon flow over East Asia and the western North Pacific was improved in the FROALS model due to its inclusion of regional air-sea coupling. The results indicated that the simulated sea surface temperature (SSTs) resulting from the regional air-sea coupling were lower than those derived directly from the driving global model over the western North Pacific north of 15°N. These colder SSTs had both positive and negative effects. On the one hand, they strengthened the western Pacific subtropical high, which improved the simulation of the summer monsoon circulation over East Asia. On the other hand, the colder SSTs suppressed surface evaporation and favored weaker local interannual variability in the SST, which led to less summer rainfall and weaker interannual rainfall variability over the Korean Peninsula and Japan. Overall, the reference simulation performed using the FROALS model is reasonable in terms of rainfall over the land area of East Asia and will become the basis for the generation of climate change scenarios for the CORDEX East Asia domain that will be described in future reports.

Biogeochemical Modeling of the Second Rise of Oxygen

NASA Astrophysics Data System (ADS)

Smith, M. L.; Catling, D.; Claire, M.; Zahnle, K.

2014-03-01

The rise of atmospheric oxygen set the tempo for the evolution of complex life on Earth. Oxygen levels are thought to have increased in two broad steps: one step occurred in the Archean ~ 2.45 Ga (the Great Oxidation Event or GOE), and another step occured in the Neoproterozoic ~750-580 Ma (the Neoprotoerozoic Oxygenation Event or NOE). During the NOE, oxygen levels increased from ~1-10% of the present atmospheric level (PAL) (Holland, 2006), to ~15% PAL in the late Neoproterozoic, to ~100% PAL later in the Phanerozoic. Complex life requires O2, so this transition allowed complex life to evolve. We seek to understand what caused the NOE. To explore causes for the NOE, we build upon the biogeochemical model of Claire et al. (2006), which calculates the redox evolution of the atmosphere, ocean, biosphere, and crust in the Archean through to the early Proterozoic. In this model, the balance between oxygenconsuming and oyxgen-producing fluxes evolves over time such that at ~2.4 Ga, the rapidly acting sources of oxygen outweigh the rapidly-acting sinks. Or, in other words, at ~2.4 Ga, the flux of oxygen from organic carbon burial exceeds the sinks of oxygen from reaction with reduced volcanic and metamoprphic gases. The model is able to drive oxygen levels to 1-10% PAL in the Proterozoic; however, the evolving redox fluxes in the model cannot explain how oxygen levels pushed above 1-10% in the late Proterozoic. The authors suggest that perhaps another buffer, such as sulfur, is needed to describe Proterozoic and Phanerozoic redox evolution. Geologic proxies show that in the Proterozoic, up to 10% of the deep ocean may have been sulfidic. With this ocean chemistry, the global sulfur cycle would have worked differently than it does today. Because the sulfur and oxygen cycles interact, the oxygen concentration could have permanently changed due to an evolving sulfur cycle (in combination with evolving redox fluxes associated with other parts of the oxygen cycle and carbon cycles). To determine how fluxes of sulfur, carbon, and oxygen define oxygen levels before, during, and after the NOE, we add a sulfur cycle to the biogeochemical model of Claire et al. (2006). Understanding processes that impact the evolution of atmospheric oxygen on Earth is key to diagnosing the habitability of other planets because it is possible that other planets undergo a similar evolution. If a sulfidic deep ocean was instrumental in driving oxygen levels to modern values, then it would be valuable to remotely detect a sulfide-rich ocean on another planet. One such remotely-detectable signature could be the color of a sulfide-rich ocean. For example, Gallardo and Espinoza (2008) have hypothesized that a sulfidic ocean may be have been blacker in color. Even if a sulfidic ocean is not key to oxygenation, detecting a planet in transition--that is, a planet with intermediate levels of oxygen co-existing with higher levels of reduced gases - would be important for diagnosing habitability.

A numerical model investigation of the formation and persistence of an erosion hotspot

USGS Publications Warehouse

Hansen, Jeff E.; Elias, Edwin; List, Jeffrey H.; Barnard, Patrick L.

2011-01-01

A Delft3D-SWAN coupled flow and wave model was constructed for the San Francisco Bight with high-resolution at 7 km-long Ocean Beach, a high-energy beach located immediately south of the Golden Gate, the sole entrance to San Francisco Bay. The model was used to investigate tidal and wave-induced flows, basic forcing terms, and potential sediment transport in an area in the southern portion of Ocean Beach that has eroded significantly over the last several decades. The model predicted flow patterns that were favorable for sediment removal from the area and net erosion from the surf-zone. Analysis of the forcing terms driving surf-zone flows revealed that wave refraction over an exposed wastewater outfall pipe between the 12 and 15 m isobaths introduces a perturbation in the wave field that results in erosion-causing flows. Modeled erosion agreed well with five years of topographic survey data from the area.

Use of Advanced Meteorological Model Output for Coastal Ocean Modeling in Puget Sound

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yang, Zhaoqing; Khangaonkar, Tarang; Wang, Taiping

2011-06-01

It is a great challenge to specify meteorological forcing in estuarine and coastal circulation modeling using observed data because of the lack of complete datasets. As a result of this limitation, water temperature is often not simulated in estuarine and coastal modeling, with the assumption that density-induced currents are generally dominated by salinity gradients. However, in many situations, temperature gradients could be sufficiently large to influence the baroclinic motion. In this paper, we present an approach to simulate water temperature using outputs from advanced meteorological models. This modeling approach was applied to simulate annual variations of water temperatures of Pugetmore » Sound, a fjordal estuary in the Pacific Northwest of USA. Meteorological parameters from North American Region Re-analysis (NARR) model outputs were evaluated with comparisons to observed data at real-time meteorological stations. Model results demonstrated that NARR outputs can be used to drive coastal ocean models for realistic simulations of long-term water-temperature distributions in Puget Sound. Model results indicated that the net flux from NARR can be further improved with the additional information from real-time observations.« less

Tide, Ocean and Climate on Exoplanets

NASA Astrophysics Data System (ADS)

Si, Y.; Yang, J.

2017-12-01

On Earth, tide is a main part of the driving force for the deep ocean overturning circulation. For habitable planets around low-mass stars, the tidal force is expected to be much stronger than that on Earth, due to the fact that the habitable zone is very close to the host stars and that tide force is inversely proportional to the orbital distance cubed. The deep ocean overturning circulation on this type of planets is therefore expected to be much stronger than that on Earth, if all else being equal. We test this hypothesis using a fully coupled atmosphere-ocean model, the Community Climate System Model version 3 (CCSM3). Our results show that the intensity of oceanic meridional overturning circulation (MOC) is approximately proportional to κ1/3, where κ is the mixing coefficient across density interfaces and it is mainly determined by the strength of the tidal force. As a result of the enhanced MOC, more heat is transported to dark regions and sea ice melts completely there, and meanwhile more heat is mixed from the surface to the deep ocean and thereby the entire ocean becomes much warmer (Fig. 1). A positive cloud feedback further warms the global ocean and atmosphere. These results imply that one planet with a stronger tidal force will likely enter a globally ice-covered snowball state at a lower stellar flux and enter a moist greenhouse or runaway greenhouse state at also a lower stellar flux, meaning that the tidal force acts to push the habitable zone outward. This study significantly improves our understanding of the possible coupling between planetary orbit, ocean, climate, and habitability on exoplanets.

Climate sensitivity to Arctic seaway restriction during the early Paleogene

NASA Astrophysics Data System (ADS)

Roberts, Christopher D.; LeGrande, Allegra N.; Tripati, Aradhna K.

2009-09-01

The opening and closing of ocean gateways affects the global distribution of heat, salt, and moisture, potentially driving climatic change on regional to global scales. Between 65 and 45 million years ago (Ma), during the early Paleogene, exchange between the Arctic and global oceans occurred through two narrow and shallow seaways, the Greenland-Norway seaway and the Turgai Strait. Sediments from the Arctic Ocean suggest that, during this interval, the surface ocean was warm, brackish, and episodically enabled the freshwater fern Azolla to bloom. The precise mechanisms responsible for the development of these conditions in the Paleogene Arctic remain uncertain. Here we show results from an isotope-enabled, atmosphere-ocean general circulation model, which indicate that Northern Hemisphere climate would have been very sensitive to the degree of oceanic exchange through the Arctic seaways. We also present modelled estimates of seawater and calcite δ18O for the Paleogene. By restricting these seaways, we simulate freshening of the surface Arctic Ocean to ~ 6 psu and warming of sea-surface temperatures by 2 °C in the North Atlantic and 5-10 °C in the Labrador Sea. Our results may help explain the occurrence of low-salinity tolerant taxa in the Arctic Ocean during the Eocene and provide a mechanism for enhanced warmth in the north western Atlantic. We propose that the formation of a volcanic land-bridge between Greenland and Europe could have caused increased ocean convection and warming of intermediate waters in the Atlantic. If true, this result is consistent with the theory that bathymetry changes may have caused thermal destabilisation of methane clathrates and supports a tectonic trigger hypothesis for the Paleocene Eocene Thermal Maximum (PETM).

Global Ocean Circulation During Cretaceous Time

NASA Astrophysics Data System (ADS)

Haupt, B. J.; Seidov, D.

2001-12-01

Present--day global thermohaline ocean circulation (TOC) is usually associated with high--latitude deep-water formation due to surface cooling. In this understanding of the TOC driven by the deep--water production, the warm deep ocean during Mesozoic--Cenozoic time is a challenge. It may be questioned whether warm deep--ocean water, which is direct geologic evidence, does reflect warm polar surface--ocean regions. For the warm Cretaceous, it is difficult to maintain strong poleward heat transport in the case of reduced oceanic thermal contrasts. Usually, atmospheric feedbacks, in conjunction with the increase of atmospheric concentrations of greenhouse gases, are employed in order to explain the warm equable Cretaceous--Eocene climate. However, there is no feasible physical mechanism that could maintain warm subpolar surface oceans in both hemispheres, an assumption often used in atmospheric modeling. Our numerical experiments indicate that having a relatively cool but saltier high--latitude sea surface in at least one hemisphere is sufficient for driving a strong meridional overturning. Thus freshwater impacts in the high latitudes may be responsible for a vigorous conveyor capable of maintaining sufficient poleward oceanic heat transport needed to keep the polar oceans ice--free. These results imply that evaporation-precipitation patterns during warm climates are especially important climatic factors that can redistribute freshwater to create hemispheric asymmetry of sea surface conditions capable of generating a sufficiently strong TOC, otherwise impossible in warm climates.

The frequency response of a coupled ice sheet-ice shelf-ocean system to climate forcing variability

NASA Astrophysics Data System (ADS)

Goldberg, D.; Snow, K.; Jordan, J. R.; Holland, P.; Arthern, R. J.

2017-12-01

Changes at the West Antarctic ice-ocean boundary in recent decades has triggered significant increases in the regions contribution to global sea-level rise, coincident with large scale, and in some cases potentially unstable, grounding line retreat. Much of the induced change is thought to be driven by fluctuations in the oceanic heat available at the ice-ocean boundary, transported on-shelf via warm Circumpolar Deep Water (CDW). However, the processes in which ocean heat drives ice-sheet loss remains poorly understood, with observational studies routinely hindered by the extreme environment notorious to the Antarctic region. In this study we apply a novel synchronous coupled ice-ocean model, developed within the MITgcm, and are thus able to provide detailed insight into the impacts of short time scale (interannual to decadal) climate variability and feedbacks within the ice-ocean system. Feedbacks and response are assessed in an idealised ice-sheet/ocean-cavity configuration in which the far field ocean condition is adjusted to emulate periodic climate variability patterns. We reveal a non-linear response of the ice-sheet to periodic variations in thermocline depth. These non-linearities illustrate the heightened sensitivity of fast flowing ice-shelves to periodic perturbations in heat fluxes occurring at interannual and decadal time scales. The results thus highlight how small perturbations in variable climate forcing, like that of ENSO, may trigger large changes in ice-sheet response.

Ocean Surface Winds Drive Dynamics of Transoceanic Aerial Movements

PubMed Central

Felicísimo, Ángel M.; Muñoz, Jesús; González-Solis, Jacob

2008-01-01

Global wind patterns influence dispersal and migration processes of aerial organisms, propagules and particles, which ultimately could determine the dynamics of colonizations, invasions or spread of pathogens. However, studying how wind-mediated movements actually happen has been hampered so far by the lack of high resolution global wind data as well as the impossibility to track aerial movements. Using concurrent data on winds and actual pathways of a tracked seabird, here we show that oceanic winds define spatiotemporal pathways and barriers for large-scale aerial movements. We obtained wind data from NASA SeaWinds scatterometer to calculate wind cost (impedance) models reflecting the resistance to the aerial movement near the ocean surface. We also tracked the movements of a model organism, the Cory's shearwater (Calonectris diomedea), a pelagic bird known to perform long distance migrations. Cost models revealed that distant areas can be connected through “wind highways” that do not match the shortest great circle routes. Bird routes closely followed the low-cost “wind-highways” linking breeding and wintering areas. In addition, we found that a potential barrier, the near surface westerlies in the Atlantic sector of the Intertropical Convergence Zone (ITCZ), temporally hindered meridional trans-equatorial movements. Once the westerlies vanished, birds crossed the ITCZ to their winter quarters. This study provides a novel approach to investigate wind-mediated movements in oceanic environments and shows that large-scale migration and dispersal processes over the oceans can be largely driven by spatiotemporal wind patterns. PMID:18698354

Climate-driven seasonal geocenter motion during the GRACE period

NASA Astrophysics Data System (ADS)

Zhang, Hongyue; Sun, Yu

2018-03-01

Annual cycles in the geocenter motion time series are primarily driven by mass changes in the Earth's hydrologic system, which includes land hydrology, atmosphere, and oceans. Seasonal variations of the geocenter motion have been reliably determined according to Sun et al. (J Geophys Res Solid Earth 121(11):8352-8370, 2016) by combining the Gravity Recovery And Climate Experiment (GRACE) data with an ocean model output. In this study, we reconstructed the observed seasonal geocenter motion with geophysical model predictions of mass variations in the polar ice sheets, continental glaciers, terrestrial water storage (TWS), and atmosphere and dynamic ocean (AO). The reconstructed geocenter motion time series is shown to be in close agreement with the solution based on GRACE data supporting with an ocean bottom pressure model. Over 85% of the observed geocenter motion time series, variance can be explained by the reconstructed solution, which allows a further investigation of the driving mechanisms. We then demonstrated that AO component accounts for 54, 62, and 25% of the observed geocenter motion variances in the X, Y, and Z directions, respectively. The TWS component alone explains 42, 32, and 39% of the observed variances. The net mass changes over oceans together with self-attraction and loading effects also contribute significantly (about 30%) to the seasonal geocenter motion in the X and Z directions. Other contributing sources, on the other hand, have marginal (less than 10%) impact on the seasonal variations but introduce a linear trend in the time series.

Ocean surface winds drive dynamics of transoceanic aerial movements.

PubMed

Felicísimo, Angel M; Muñoz, Jesús; González-Solis, Jacob

2008-08-13

Global wind patterns influence dispersal and migration processes of aerial organisms, propagules and particles, which ultimately could determine the dynamics of colonizations, invasions or spread of pathogens. However, studying how wind-mediated movements actually happen has been hampered so far by the lack of high resolution global wind data as well as the impossibility to track aerial movements. Using concurrent data on winds and actual pathways of a tracked seabird, here we show that oceanic winds define spatiotemporal pathways and barriers for large-scale aerial movements. We obtained wind data from NASA SeaWinds scatterometer to calculate wind cost (impedance) models reflecting the resistance to the aerial movement near the ocean surface. We also tracked the movements of a model organism, the Cory's shearwater (Calonectris diomedea), a pelagic bird known to perform long distance migrations. Cost models revealed that distant areas can be connected through "wind highways" that do not match the shortest great circle routes. Bird routes closely followed the low-cost "wind-highways" linking breeding and wintering areas. In addition, we found that a potential barrier, the near surface westerlies in the Atlantic sector of the Intertropical Convergence Zone (ITCZ), temporally hindered meridional trans-equatorial movements. Once the westerlies vanished, birds crossed the ITCZ to their winter quarters. This study provides a novel approach to investigate wind-mediated movements in oceanic environments and shows that large-scale migration and dispersal processes over the oceans can be largely driven by spatiotemporal wind patterns.

Geophysical Age Dating of Seamounts using Dense Core Flexure Model

NASA Astrophysics Data System (ADS)

Hwang, Gyuha; Kim, Seung-Sep

2016-04-01

Lithospheric flexure of oceanic plate is thermo-mechanical response of an elastic plate to the given volcanic construct (e.g., seamounts and ocean islands). If the shape and mass of such volcanic loads are known, the flexural response is governed by the thickness of elastic plate, Te. As the age of oceanic plate increases, the elastic thickness of oceanic lithosphere becomes thicker. Thus, we can relate Te with the age of plate at the time of loading. To estimate the amount of the driving force due to seamounts on elastic plate, one needs to approximate their density structure. The most common choice is uniform density model, which utilizes constant density value for a seamount. This approach simplifies computational processes for gravity prediction and error estimates. However, the uniform density model tends to overestimate the total mass of the seamount and hence produces more positive gravitational contributions from the load. Minimization of gravity misfits using uniform density, therefore, favors thinner Te in order to increase negative contributions from the lithospheric flexure, which can compensate for the excessive positives from the seamount. An alternative approach is dense core model, which approximate the heterogeneity nature of seamount density as three bodies of infill sediment, edifice, and dense core. In this study, we apply the dense core model to the Louisville Seamount Chain for constraining flexural deformation. We compare Te estimates with the loading time of the examined seamounts to redefine empirical geophysical age dating of seamounts.

Testing a common ice-ocean parameterization with laboratory experiments

NASA Astrophysics Data System (ADS)

McConnochie, C. D.; Kerr, R. C.

2017-07-01

Numerical models of ice-ocean interactions typically rely upon a parameterization for the transport of heat and salt to the ice face that has not been satisfactorily validated by observational or experimental data. We compare laboratory experiments of ice-saltwater interactions to a common numerical parameterization and find a significant disagreement in the dependence of the melt rate on the fluid velocity. We suggest a resolution to this disagreement based on a theoretical analysis of the boundary layer next to a vertical heated plate, which results in a threshold fluid velocity of approximately 4 cm/s at driving temperatures between 0.5 and 4°C, above which the form of the parameterization should be valid.

Local atmospheric response to warm mesoscale ocean eddies in the Kuroshio-Oyashio Confluence region.

PubMed

Sugimoto, Shusaku; Aono, Kenji; Fukui, Shin

2017-09-19

In the extratropical regions, surface winds enhance upward heat release from the ocean to atmosphere, resulting in cold surface ocean: surface ocean temperature is negatively correlated with upward heat flux. However, in the western boundary currents and eddy-rich regions, the warmer surface waters compared to surrounding waters enhance upward heat release-a positive correlation between upward heat release and surface ocean temperature, implying that the ocean drives the atmosphere. The atmospheric response to warm mesoscale ocean eddies with a horizontal extent of a few hundred kilometers remains unclear because of a lack of observations. By conducting regional atmospheric model experiments, we show that, in the Kuroshio-Oyashio Confluence region, wintertime warm eddies heat the marine atmospheric boundary layer (MABL), and accelerate westerly winds in the near-surface atmosphere via the vertical mixing effect, leading to wind convergence around the eastern edge of eddies. The warm-eddy-induced convergence forms local ascending motion where convective precipitation is enhanced, providing diabatic heating to the atmosphere above MABL. Our results indicate that warm eddies affect not only near-surface atmosphere but also free atmosphere, and possibly synoptic atmospheric variability. A detailed understanding of warm eddy-atmosphere interaction is necessary to improve in weather and climate projections.

How do local and remote processes affect the distribution of iron in the Atlantic Ocean?

NASA Astrophysics Data System (ADS)

Tagliabue, A.; Boyd, P.; Rijkenberg, M. J. A.; Williams, R. G.

2016-02-01

Iron (Fe) plays an important role in governing the magnitudes and patterns of primary productivity, nitrogen fixation and phytoplankton community composition across the Atlantic Ocean. Variations in the supply of Fe to surface waters across the mixed layer interface, over seasonal to annual to decadal scales, are underpinned by it's vertical profile. Traditionally, nutrient profiles are understood in terms of surface depletion and subsurface regeneration, but for Fe this is more complicated due to the role of scavenging and organic complexation by ligands, as well as subsurface sources. This means that the Fe profile may be controlled locally, by sinking, regeneration and scavenging or remotely, by the upstream conditions of subducted water masses. Subduction drives the transfer of Fe across the interface between winter mixed layer and the ocean interior, but has received little attention thus far. Via the subduction of watermasses with distinct biogeochemical signatures to low latitudes, remote processes can regulate the Atlantic Ocean Fe distribution at local scales. Specifically, the formation of mode waters with excess Fe binding ligands (positive L*) enable these waters to stabilise any Fe flux from regeneration that would otherwise be lost by scavenging. The pattern of mode water ventilation then highlights those regions of the ocean where local processes are able to influence the Fe profile. Local process that augment L*, such as the production of ligands during particle regeneration, can also interact with the larger scale ventilation signature but do not alter the main trends. By applying our framework to recent GEOTRACES datasets over the Atlantic Ocean we are able to highlight regions where the Fe profile is forced locally or remotely, thereby providing an important process-based constraint on the biogeochemical models we rely on for future projections. Furthermore, we are able to appraise how the varying influence of local and remote processes drives the degree of agreement in the vertical profiles of Fe and macronutrients, which then sets the degree of surface water Fe limitation.

Tree-Structured Methods for Prediction and Data Visualization

DTIC Science & Technology

2009-03-18

which variables are most important for predicting smoking abstinence . GUIDE, on the other hand, can model interactions of any order. Fur- ther, it...tree for predicting smoking abstinence after one week of treatment. An observation goes to the left node if and only if the stated condition is...H. E., and Loh, W.-Y. (2009). Which surface atmospheric variable drives the seasonal cycle of sea surface temperature over the global ocean

Ocean-atmosphere coupling at the Brazil-Malvinas Confluence region based on in situ, satellite and numerical model data

NASA Astrophysics Data System (ADS)

Casagrande, F.; Souza, R.; Pezzi, L.

2013-05-01

In the Southwest Atlantic close to 40oS, the meeting of two ocean currents with distinct characteristics, the Brazil Current (BC), warm and saline, and the Malvinas Current (MC), cold and low salinity, resulting in strong activity marked by the formation of mesoscale eddies, this region is known as Brazil Malvinas Confluence (BMC). The INTERCONF project (Ocean Atmosphere Interaction over the region of CBM) perfoms since the 2002 data collection in situ radiosondes and XBTs onboard the Oceanographic Support Ship Ary Rongel during its trajectory of Brazil to the Antarctic continent. This paper analyzes the thermal contrast and ocean atmosphere coupling on the ocean front from the INTERCONF data, and compares the results to satellite data (QuikSCAT) and numerical models (Eta-CPTEC / INPE). The results indicate that the Sea Surface Temperature (SST) is driving the atmosphere, on the warm waters of the BC occurs an intensification of the winds and heat fluxes, and the reverse occurs on the cold waters of the MC. The data collected in 2009 include the presence of a warm core eddy (42 oS to 43.1 oS) which recorded higher values of heat fluxes and wind speed in relation to its surroundings. On the warm core eddy wind speed recorded was about 10 m.s-1, while on the BC and MC was approximately 7 m.s-1 and 2 m.s-1, respectively. Satellite data and numerical model tends to overestimate the wind speed data in the region in relation to data collected in situ. The heat flux data from the numerical model tend to increase over the warm waters and cold waters on the decline, though the amounts recorded by the model have low correlation.

Effects of Whaling on the Structure of the Southern Ocean Food Web: Insights on the “Krill Surplus” from Ecosystem Modelling

PubMed Central

Surma, Szymon; Pakhomov, Evgeny A.; Pitcher, Tony J.

2014-01-01

The aim of this study was to examine the ecological plausibility of the “krill surplus” hypothesis and the effects of whaling on the Southern Ocean food web using mass-balance ecosystem modelling. The depletion trajectory and unexploited biomass of each rorqual population in the Antarctic was reconstructed using yearly catch records and a set of species-specific surplus production models. The resulting estimates of the unexploited biomass of Antarctic rorquals were used to construct an Ecopath model of the Southern Ocean food web existing in 1900. The rorqual depletion trajectory was then used in an Ecosim scenario to drive rorqual biomasses and examine the “krill surplus” phenomenon and whaling effects on the food web in the years 1900–2008. An additional suite of Ecosim scenarios reflecting several hypothetical trends in Southern Ocean primary productivity were employed to examine the effect of bottom-up forcing on the documented krill biomass trend. The output of the Ecosim scenarios indicated that while the “krill surplus” hypothesis is a plausible explanation of the biomass trends observed in some penguin and pinniped species in the mid-20th century, the excess krill biomass was most likely eliminated by a rapid decline in primary productivity in the years 1975–1995. Our findings suggest that changes in physical conditions in the Southern Ocean during this time period could have eliminated the ecological effects of rorqual depletion, although the mechanism responsible is currently unknown. Furthermore, a decline in iron bioavailability due to rorqual depletion may have contributed to the rapid decline in overall Southern Ocean productivity during the last quarter of the 20th century. The results of this study underscore the need for further research on historical changes in the roles of top-down and bottom-up forcing in structuring the Southern Ocean food web. PMID:25517505

Effects of whaling on the structure of the Southern Ocean food web: insights on the "krill surplus" from ecosystem modelling.

PubMed

Surma, Szymon; Pakhomov, Evgeny A; Pitcher, Tony J

2014-01-01

The aim of this study was to examine the ecological plausibility of the "krill surplus" hypothesis and the effects of whaling on the Southern Ocean food web using mass-balance ecosystem modelling. The depletion trajectory and unexploited biomass of each rorqual population in the Antarctic was reconstructed using yearly catch records and a set of species-specific surplus production models. The resulting estimates of the unexploited biomass of Antarctic rorquals were used to construct an Ecopath model of the Southern Ocean food web existing in 1900. The rorqual depletion trajectory was then used in an Ecosim scenario to drive rorqual biomasses and examine the "krill surplus" phenomenon and whaling effects on the food web in the years 1900-2008. An additional suite of Ecosim scenarios reflecting several hypothetical trends in Southern Ocean primary productivity were employed to examine the effect of bottom-up forcing on the documented krill biomass trend. The output of the Ecosim scenarios indicated that while the "krill surplus" hypothesis is a plausible explanation of the biomass trends observed in some penguin and pinniped species in the mid-20th century, the excess krill biomass was most likely eliminated by a rapid decline in primary productivity in the years 1975-1995. Our findings suggest that changes in physical conditions in the Southern Ocean during this time period could have eliminated the ecological effects of rorqual depletion, although the mechanism responsible is currently unknown. Furthermore, a decline in iron bioavailability due to rorqual depletion may have contributed to the rapid decline in overall Southern Ocean productivity during the last quarter of the 20th century. The results of this study underscore the need for further research on historical changes in the roles of top-down and bottom-up forcing in structuring the Southern Ocean food web.

The amplifying influence of increased ocean stratification on a future year without a summer.

PubMed

Fasullo, J T; Tomas, R; Stevenson, S; Otto-Bliesner, B; Brady, E; Wahl, E

2017-10-31

In 1816, the coldest summer of the past two centuries was observed over northeastern North America and western Europe. This so-called Year Without a Summer (YWAS) has been widely attributed to the 1815 eruption of Indonesia's Mt. Tambora and was concurrent with agricultural failures and famines worldwide. To understand the potential impacts of a similar future eruption, a thorough physical understanding of the YWAS is crucial. Climate model simulations of both the 1815 Tambora eruption and a hypothetical analogous future eruption are examined, the latter occurring in 2085 assuming a business-as-usual climate scenario. Here, we show that the 1815 eruption drove strong responses in both the ocean and cryosphere that were fundamental to driving the YWAS. Through modulation of ocean stratification and near-surface winds, global warming contributes to an amplified surface climate response. Limitations in using major volcanic eruptions as a constraint on cloud feedbacks are also found.

The impact of glacier geometry on meltwater plume structure and submarine melt in Greenland fjords

NASA Astrophysics Data System (ADS)

Carroll, D.; Sutherland, D. A.; Hudson, B.; Moon, T.; Catania, G. A.; Shroyer, E. L.; Nash, J. D.; Bartholomaus, T. C.; Felikson, D.; Stearns, L. A.; Noël, B. P. Y.; Broeke, M. R.

2016-09-01

Meltwater from the Greenland Ice Sheet often drains subglacially into fjords, driving upwelling plumes at glacier termini. Ocean models and observations of submarine termini suggest that plumes enhance melt and undercutting, leading to calving and potential glacier destabilization. Here we systematically evaluate how simulated plume structure and submarine melt during summer months depends on realistic ranges of subglacial discharge, glacier depth, and ocean stratification from 12 Greenland fjords. Our results show that grounding line depth is a strong control on plume-induced submarine melt: deep glaciers produce warm, salty subsurface plumes that undercut termini, and shallow glaciers produce cold, fresh surface-trapped plumes that can overcut termini. Due to sustained upwelling velocities, plumes in cold, shallow fjords can induce equivalent depth-averaged melt rates compared to warm, deep fjords. These results detail a direct ocean-ice feedback that can affect the Greenland Ice Sheet.

Role of tropical Indian and Atlantic Oceans variability on ENSO

NASA Astrophysics Data System (ADS)

Prodhomme, Chloé; Terray, Pascal; Masson, Sebastien; Boschat, Ghyslaine

2014-05-01

There are strong evidences of an interaction between tropical Indian, Atlantic and Pacific Oceans. Nevertheless, these interactions remain deeply controversial. While some authors claim the tropical Indian and Atlantic oceans only play a passive role with respect to ENSO, others suggest a driving role for these two basins on ENSO. The mecanisms underlying these relations are not fully understood and, in the Indian Ocean, the possible role of both modes of tropical variability (the Indian Ocean Dipole (IOD) and the Indian Ocean Basin mode (IOB)) remain unclear. To better quantify and understand how the variability of the tropical Indian and Atlantic Oceans impact ENSO variability, we performed two sensitivity experiments using the SINTEX-F2 coupled model. For each experiment, we suppressed the variability of SST and the air-sea coupling in either the tropical Indian Ocean or tropical Atlantic Ocean by applying a strong nudging of the SST to the observed SST climatology. In both experiments, the ENSO periodicity increases. In the Atlantic experiment, our understanding of this increased periodicity is drastically limited by the strongly biased mean state in this region. Conversely, in the Indian Ocean experiment, the increase of ENSO periodicity is related to the absence of the IOB following the El Niño peak, which leads to a decrease of westerly winds in the western Pacific during late winter and spring after the peak. These weaker westerlies hinders the transition to a La Niña phase and thus increase the duration and periodicity of the event.

Seasonal and Interannual Variability of the Arctic Sea Ice: A Comparison between AO-FVCOM and Observations

NASA Astrophysics Data System (ADS)

Zhang, Y.; Chen, C.; Beardsley, R. C.; Gao, G.; Qi, J.; Lin, H.

2016-02-01

A high-resolution (up to 2 km), unstructured-grid, fully ice-sea coupled Arctic Ocean Finite-Volume Community Ocean Model (AO-FVCOM) was used to simulate the Arctic sea ice over the period 1978-2014. Good agreements were found between simulated and observed sea ice extent, concentration, drift velocity and thickness, indicating that the AO-FVCOM captured not only the seasonal and interannual variability but also the spatial distribution of the sea ice in the Arctic in the past 37 years. Compared with other six Arctic Ocean models (ECCO2, GSFC, INMOM, ORCA, NAME and UW), the AO-FVCOM-simulated ice thickness showed a higher correlation coefficient and a smaller difference with observations. An effort was also made to examine the physical processes attributing to the model-produced bias in the sea ice simulation. The error in the direction of the ice drift velocity was sensitive to the wind turning angle; smaller when the wind was stronger, but larger when the wind was weaker. This error could lead to the bias in the near-surface current in the fully or partially ice-covered zone where the ice-sea interfacial stress was a major driving force.

Isostasy as a Driver of Paleo Retreat of the Greenland Ice Sheet

NASA Astrophysics Data System (ADS)

Robinson, A.; Tabone, I.; Alvarez-Solas, J.; Montoya, M.

2016-12-01

During glacial times, the Greenland ice sheet (GrIS) extended onto the continental shelf, and thus was much more directly affected by changing ocean temperatures through basal melt of the marine ice margins than it is today. The larger glacial ice sheet also induced lithospheric depression of several hundred meters in regions that are near sea level today. As the ice sheet retreated inland under interglacial climatic forcing, the regions significantly affected by local isostatic changes in elevation were exposed to much higher basal melt rates than they would have been given the present-day topography. Here we explore this effect using a hybrid ice sheet model that represents both grounded and floating ice, as well as local isostatic effects, and is driven by both atmospheric and oceanic temperature anomalies. We find that when transient oceanic forcing is included in the model, isostasy plays an important role in allowing oceanic melting to drive GrIS retreat in some regions. During the last interglacial, for example, this effect can account for a significant additional sea-level contribution, as well as an increase in the rate of sea-level rise. Our results highlight the importance of accounting for ice-ocean-lithosphere interactions in the past, in order to be able to properly reconstruct the evolution of the ice sheet, and for estimating its sensitivity to potential changes in climate in the future.

The Southern Ocean as a driver of centennial to millenial timescale radiocarbon variations

NASA Astrophysics Data System (ADS)

Rodgers, K. B.; Bianchi, D.; Galbraith, E.; Gnanadesikan, A.; Iudicone, D.; Mikaloff Fletcher, S.; Sarmiento, J. L.; Slater, R. D.

2009-04-01

Paleo-proxy records reveal large delta-c14 variations for both the atmosphere and the ocean on centennial to millenial timescales. One of the most pronounced examples is the onset phase of the Younger Dryas, when atmospheric delta-c14 rose by 70 per mil in only 200 years. Another is the most recent deglaciation (and the associated "Mystery Interval"). Many of the significant centennial to millenial transients in atmospheric delta-c14 are reflected in ocean interior delta-c14 at intermediate depths in the Pacific over the last 50kyrs. An ocean model has been used to test the idea that only modest perturbations to Southern Ocean winds provides a means to link the oceanic and atmospheric delta-c14 variations. Perturbations to the winds over the Southern Ocean are able to drive sizable decoupling of the fluxes of 14CO2 and 12CO2 over the Southern Ocean, thus modifying atmospheric delta-c14. These same perturbations are able to perturb rapidly the depth of intermediate water horizons in the North Pacific through the passage of baroclinic planetary (Rossby) waves. This sensitivity is significantly stronger than what previous studies have found for perturbations to the Meridional Overturning Circulation (MOC) in the North Atlantic. It is suggested that delta-c14 may provide a powerful tracer for understanding past variations in the climate system.

75 FR 17743 - Ocean Transportation Intermediary License Applicants

Federal Register 2010, 2011, 2012, 2013, 2014

2010-04-07

..., Managing Member. Integres Global Logistics, Inc., 10995 Gold Center Drive, Suite 120, Rancho Cordova, CA..., DC 20573. Non-Vessel-Operating Common Carrier--Ocean Transportation Intermediary: HPK Logistics (USA... (Qualifying Individual) Jian Sun, President. Cargo Logistics International, LLC, 8761 Dorchester Road, Suite...

The North Atlantic Oscillation as a driver of multidecadal variability of the AMOC, the AMO, and Northern Hemisphere climate

NASA Astrophysics Data System (ADS)

Delworth, T. L.; Zeng, F. J.; Yang, X.; Zhang, L.

2017-12-01

We use suites of simulations with coupled ocean-atmosphere models to show that multidecadal changes in the North Atlantic Oscillation (NAO) can drive multidecadal changes in the Atlantic Meridional Overturning Circulation (AMOC) and the Atlantic Multidecadal Oscillation (AMO), with associated hemispheric climatic impacts. These impacts include rapid changes in Arctic sea ice, hemispheric temperature, and modulation of Atlantic hurricane activity. We use models that incorporate either a fully dynamic ocean or a simple slab ocean to explore the role of ocean dynamics and ocean-atmosphere interactions. A positive phase of the NAO is associated with strengthened westerly winds over the North Atlantic. These winds extract more heat than normal from the subpolar ocean, thereby increasing upper ocean density, deepwater formation, and the strength of the AMOC and associated poleward ocean heat transport. This warming leads to a positive phase of the AMO. The enhanced oceanic heat transport extends to the Arctic where it causes a reduction of Arctic sea ice. Large-scale atmospheric warming reduces vertical wind shear in the tropical North Atlantic, creating an environment more favorable for tropical storms. We use models to further show that observed multidecadal variations of the NAO over the 20th and early 21st centuries may have led to multidecadal variations of simulated AMOC and the AMO. Specifically, negative NAO values from the late 1960s through the early 1980s led to a weakened AMOC/cold North Atlantic, whereas increasing NAO values from the late 1980s through the late 1990s increased the model AMOC and led to a positive (warm) phase of the AMO. The warm phase contributed to increases in tropical storm activity and decreases in Arctic sea ice after the mid 1990s. Ocean dynamics are essential for translating the observed NAO variations into ocean heat content variations for the extratropical North Atlantic, but appear less important in the tropical North Atlantic. The observed AMO has substantial SST amplitude in both the tropical and extratropical North Atlantic. These results suggest that additional factors, such as cloud feedback, dust feedback, and anthropogenic radiative forcing, may play a crucial role for the tropical expression of the AMO.

Parallel Computation of Ocean-Atmosphere-Wave Coupled Storm Surge Model

NASA Astrophysics Data System (ADS)

Kim, K.; Yamashita, T.

2003-12-01

Ocean-atmosphere interactions are very important in the formation and development of tropical storms. These interactions are dominant in exchanging heat, momentum, and moisture fluxes. Heat flux is usually computed using a bulk equation. In this equation air-sea interface supplies heat energy to the atmosphere and to the storm. Dynamical interaction is most often one way in which it is the atmosphere that drives the ocean. The winds transfer momentum to both ocean surface waves and ocean current. The wind wave makes an important role in the exchange of the quantities of motion, heat and a substance between the atmosphere and the ocean. Storm surges can be considered as the phenomena of mean sea-level changes, which are the result of the frictional stresses of strong winds blowing toward the land and causing the set level and the low atmospheric pressure at the centre of the cyclone can additionally raise the sea level. In addition to the rise in water level itself, another wave factor must be considered. A rise of mean sea level due to white-cap wave dissipation should be considered. In bounded bodies of water, such as small seas, wind driven sea level set up is much serious than inverted barometer effects, in which the effects of wind waves on wind-driven current play an important role. It is necessary to develop the coupled system of the full spectral third-generation wind-wave model (WAM or WAVEWATCH III), the meso-scale atmosphere model (MM5) and the coastal ocean model (POM) for simulating these physical interactions. As the component of coupled system is so heavy for personal usage, the parallel computing system should be developed. In this study, first, we developed the coupling system of the atmosphere model, ocean wave model and the coastal ocean model, in the Beowulf System, for the simulation of the storm surge. It was applied to the storm surge simulation caused by Typhoon Bart (T9918) in the Yatsushiro Sea. The atmosphere model and the ocean model have been made the parallel codes by SPMD methods. The wave-current interface model was developed by defining the wave breaking stresses. And we developed the coupling program to collect and distribute the exchanging data with the parallel system. Every models and coupler are executed at same time, and they calculate own jobs and pass data with organic system. MPMD method programming was performed to couple the models. The coupler and each models united by the separated group, and they calculated by the group unit. Also they passed message when exchanging data by global unit. The data are exchanged every 60-second model time that is the least common multiple time of the atmosphere model, the wave model and the ocean model. The model was applied to the storm surge simulation in the Yatsushiro Sea, in which we could not simulated the observed maximum surge height with the numerical model that did not include the wave breaking stress. It is confirmed that the simulation which includes the wave breaking stress effects can produce the observed maximum height, 450 cm, at Matsuai.

The Effects of Interactive Stratospheric Chemistry on Antarctic and Southern Ocean Climate Change in an AOGCM

NASA Technical Reports Server (NTRS)

Li, Feng; Newman, Paul; Pawson, Steven; Waugh, Darryn

2014-01-01

Stratospheric ozone depletion has played a dominant role in driving Antarctic climate change in the last decades. In order to capture the stratospheric ozone forcing, many coupled atmosphere-ocean general circulation models (AOGCMs) prescribe the Antarctic ozone hole using monthly and zonally averaged ozone field. However, the prescribed ozone hole has a high ozone bias and lacks zonal asymmetry. The impacts of these biases on model simulations, particularly on Southern Ocean and the Antarctic sea ice, are not well understood. The purpose of this study is to determine the effects of using interactive stratospheric chemistry instead of prescribed ozone on Antarctic and Southern Ocean climate change in an AOGCM. We compare two sets of ensemble simulations for the 1960-2010 period using different versions of the Goddard Earth Observing System 5 - AOGCM: one with interactive stratospheric chemistry, and the other with prescribed monthly and zonally averaged ozone and 6 other stratospheric radiative species calculated from the interactive chemistry simulations. Consistent with previous studies using prescribed sea surface temperatures and sea ice concentrations, the interactive chemistry runs simulate a deeper Antarctic ozone hole and consistently larger changes in surface pressure and winds than the prescribed ozone runs. The use of a coupled atmosphere-ocean model in this study enables us to determine the impact of these surface changes on Southern Ocean circulation and Antarctic sea ice. The larger surface wind trends in the interactive chemistry case lead to larger Southern Ocean circulation trends with stronger changes in northerly and westerly surface flow near the Antarctica continent and stronger upwelling near 60S. Using interactive chemistry also simulates a larger decrease of sea ice concentrations. Our results highlight the importance of using interactive chemistry in order to correctly capture the influences of stratospheric ozone depletion on climate change over Antarctic and the Southern Ocean.

Spontaneous Wave Generation from Submesoscale Fronts and Filaments

NASA Astrophysics Data System (ADS)

Shakespeare, C. J.; Hogg, A.

2016-02-01

Submesoscale features such as eddies, fronts, jets and filaments can be significant sources of spontaneous wave generation at the ocean surface. Unlike near-inertial waves forced by winds, these spontaneous waves are typically of higher frequency and can propagate through the thermocline, whereupon they break and drive mixing in the ocean interior. Here we investigate the spontaneous generation, propagation and subsequent breaking of these waves using a combination of theory and submesoscale resolving numerical models. The mechanism of generation is nearly identical to that of lee waves where flow is deflected over a rigid obstacle on the sea floor. Here, very sharp fronts and filaments of order 100m width moving in the submesoscale surface flow generate "surface lee waves" by presenting an obstacle to the surrounding stratified fluid. Using our numerical model we quantify the net downward wave energy flux from the surface, and where it is dissipated in the water column. Our results suggest an alternative to the classical paradigm where the energy associated with mixing in the ocean interior is sourced from bottom-generated lee waves.

Driving Roles of Tropospheric and Stratospheric Thermal Anomalies in Intensification and Persistence of the Arctic Superstorm in 2012

NASA Astrophysics Data System (ADS)

Tao, Wei; Zhang, Jing; Fu, Yunfei; Zhang, Xiangdong

2017-10-01

Intense synoptic-scale storms have been more frequently observed over the Arctic during recent years. Specifically, a superstorm hit the Arctic Ocean in August 2012 and preceded a new record low Arctic sea ice extent. In this study, the major physical processes responsible for the storm's intensification and persistence are explored through a series of numerical modeling experiments with the Weather Research and Forecasting model. It is found that thermal anomalies in troposphere as well as lower stratosphere jointly lead to the development of this superstorm. Thermal contrast between the unusually warm Siberia and the relatively cold Arctic Ocean results in strong troposphere baroclinicity and upper level jet, which contribute to the storm intensification initially. On the other hand, Tropopause Polar Vortex (TPV) associated with the thermal anomaly in lower stratosphere further intensifies the upper level jet and accordingly contributes to a drastic intensification of the storm. Stacking with the enhanced surface low, TPV intensifies further, which sustains the storm to linger over the Arctic Ocean for an extended period.

Turbidity Currents With Equilibrium Basal Driving Layers: A Mechanism for Long Runout

NASA Astrophysics Data System (ADS)

Luchi, R.; Balachandar, S.; Seminara, G.; Parker, G.

2018-02-01

Turbidity currents run out over 100 km in lakes and reservoirs, and over 1,000 km in the ocean. They do so without dissipating themselves via excess entrainment of ambient water. Existing layer-averaged formulations cannot capture this. We use a numerical model to describe the temporal evolution of a turbidity current toward steady state under condition of zero net sediment flux at the bed. The flow self-partitions itself into two layers. The lower "driving layer" approaches an invariant flow thickness, velocity profile, and suspended sediment concentration profile that sequesters nearly all of the suspended sediment. This layer can continue indefinitely at steady state over a constant bed slope. The upper "driven layer" contains a small fraction of the suspended sediment. The devolution of the flow into these two layers likely allows the driving layer to run out long distances.

Arctic circulation regimes

PubMed Central

Proshutinsky, Andrey; Dukhovskoy, Dmitry; Timmermans, Mary-Louise; Krishfield, Richard; Bamber, Jonathan L.

2015-01-01

Between 1948 and 1996, mean annual environmental parameters in the Arctic experienced a well-pronounced decadal variability with two basic circulation patterns: cyclonic and anticyclonic alternating at 5 to 7 year intervals. During cyclonic regimes, low sea-level atmospheric pressure (SLP) dominated over the Arctic Ocean driving sea ice and the upper ocean counterclockwise; the Arctic atmosphere was relatively warm and humid, and freshwater flux from the Arctic Ocean towards the subarctic seas was intensified. By contrast, during anticylonic circulation regimes, high SLP dominated driving sea ice and the upper ocean clockwise. Meanwhile, the atmosphere was cold and dry and the freshwater flux from the Arctic to the subarctic seas was reduced. Since 1997, however, the Arctic system has been under the influence of an anticyclonic circulation regime (17 years) with a set of environmental parameters that are atypical for this regime. We discuss a hypothesis explaining the causes and mechanisms regulating the intensity and duration of Arctic circulation regimes, and speculate how changes in freshwater fluxes from the Arctic Ocean and Greenland impact environmental conditions and interrupt their decadal variability. PMID:26347536

Constraints on the Opening Rate of Bands on Europa

NASA Technical Reports Server (NTRS)

Stempel, M. M.; Barr, A. C.; Pappalardo, R. T.

2004-01-01

The opening rates of two bands on Europa, inferred to be sites of spreading of the icy lithosphere, are constrained based on a mid-ocean ridge analog model. Estimates of brittle-ductile transition depth combined with a conductive cooling model limit active band lifetimes to 0.24 - 35 Myr and strain rates of 8.1 x 10(exp -13) - 8.2 x 10(exp -15)/s. These values suggest tensile strengths for ice on Europa of 0.46 - 2.3 MPa, consistent with nonsynchronous rotation as the dominant driving mechanism for band opening.

Modeling the basal melting and marine ice accretion of the Amery Ice Shelf

NASA Astrophysics Data System (ADS)

Galton-Fenzi, B. K.; Hunter, J. R.; Coleman, R.; Marsland, S. J.; Warner, R. C.

2012-09-01

The basal mass balance of the Amery Ice Shelf (AIS) in East Antarctica is investigated using a numerical ocean model. The main improvements of this model over previous studies are the inclusion of frazil formation and dynamics, tides and the use of the latest estimate of the sub-ice-shelf cavity geometry. The model produces a net basal melt rate of 45.6 Gt year-1 (0.74 m ice year-1) which is in good agreement with reviewed observations. The melting at the base of the ice shelf is primarily due to interaction with High Salinity Shelf Water created from the surface sea-ice formation in winter. The temperature difference between the coldest waters created in the open ocean and the in situ freezing point of ocean water in contact with the deepest part of the AIS drives a melt rate that can exceed 30 m of ice year-1. The inclusion of frazil dynamics is shown to be important for both melting and marine ice accretion (refreezing). Frazil initially forms in the supercooled water layer adjacent to the base of the ice shelf. The net accretion of marine ice is 5.3 Gt year-1, comprised of 3.7 Gt year-1 of frazil accretion and 1.6 Gt year-1 of direct basal refreezing.

Southern Ocean Convection and tropical telleconnections

NASA Astrophysics Data System (ADS)

Marinov, I.; Cabre, A.; Gnanadesikan, A.

2014-12-01

We show that Southern Ocean (SO) temperatures in the latest generation of Earth System Models exhibit two major modes of variation, one driven by deep convection, the other by tropical variability. We perform a CMIP5 model intercomparison to understand why different climate models represent SO variability so differently in long, control simulations. We show that multiyear variability in Southern Ocean sea surface temperatures (SSTs) can in turn influence oceanic and atmospheric conditions in the tropics on short (atmospheric) time-scales. We argue that the strength and pattern of SO-tropical teleconnections depends on the intensity of SO deep convection. Periodic convection in the SO is a feature of most CMIP5 models under preindustrial forcing (deLavergne et al., 2014). Models show a wide distribution in the spatial extent, periodicity and intensity of their SO convection, with some models convecting most of the time, and some showing very little convection. In a highly convective coupled model, we find that multidecadal variability in SO and global SSTs, as well as SO heat storage are driven by Weddell Sea convective variability, with convective decades relatively warm due to the heat released from the deep southern ocean and non-convective decades cold due to the subsurface storage of heat. Furthermore, pulses of SO convection drive SST and sea ice variations, influencing absorbed shortwave and emitted longwave radiation, wind, cloud and precipitation patterns, with climatic implications for the low latitudes via fast atmospheric teleconnections. We suggest that these high-low latitude teleconnection mechanisms are relevant for understanding hiatus decades. Additionally, Southern Ocean deep convection varied significantly during past, natural climate changes such as during the last deglaciation. Weddell Sea open convection was recently weakened, likely as a consequence of anthropogenic forcing and the resulting surface freshening. Our study opens up the tantalizing possibility that such large-scale changes in SO deep convection might have tropical and indeed global implications via atmospheric teleconnections. We advocate the collection of both paleo and modern proxies that can verify these model-derived mechanisms and global teleconnections.

Sustained climate warming drives declining marine biological productivity

NASA Astrophysics Data System (ADS)

Moore, J. Keith; Fu, Weiwei; Primeau, Francois; Britten, Gregory L.; Lindsay, Keith; Long, Matthew; Doney, Scott C.; Mahowald, Natalie; Hoffman, Forrest; Randerson, James T.

2018-03-01

Climate change projections to the year 2100 may miss physical-biogeochemical feedbacks that emerge later from the cumulative effects of climate warming. In a coupled climate simulation to the year 2300, the westerly winds strengthen and shift poleward, surface waters warm, and sea ice disappears, leading to intense nutrient trapping in the Southern Ocean. The trapping drives a global-scale nutrient redistribution, with net transfer to the deep ocean. Ensuing surface nutrient reductions north of 30°S drive steady declines in primary production and carbon export (decreases of 24 and 41%, respectively, by 2300). Potential fishery yields, constrained by lower–trophic-level productivity, decrease by more than 20% globally and by nearly 60% in the North Atlantic. Continued high levels of greenhouse gas emissions could suppress marine biological productivity for a millennium.

Ocean stratification reduces melt rates at the grounding zone of the Ross Ice Shelf

NASA Astrophysics Data System (ADS)

Begeman, C. B.; Tulaczyk, S. M.; Marsh, O.; Mikucki, J.; Stanton, T. P.; Hodson, T. O.; Siegfried, M. R.; Powell, R. D.; Christianson, K. A.; King, M. A.

2017-12-01

Ocean-driven melting of ice shelves is often invoked as the primary mechanism for triggering ice loss from Antarctica. However, due to the difficulty in accessing the sub-ice-shelf ocean cavity, the relationship between ice-shelf melt rates and ocean conditions is poorly understood, particularly near the transition from grounded to floating ice, known as the grounding zone. Here we present the first borehole oceanographic observations from the grounding zone of Antarctica's largest ice shelf. Contrary to predictions that tidal currents near grounding zones should mix the water column, driving high ice-shelf melt rates, we find a stratified sub-ice-shelf water column. The vertical salinity gradient dominates stratification over a weakly unstable vertical temperature gradient; thus, stratification takes the form of a double-diffusive staircase. These conditions limit vertical heat fluxes and lead to low melt rates in the ice-shelf grounding zone. While modern grounding zone melt rates may presently be overestimated in models that assume efficient tidal mixing, the high sensitivity of double-diffusive staircases to ocean freshening and warming suggests future melt rates may be underestimated, biasing projections of global sea-level rise.

Southern Ocean phytoplankton turnover in response to stepwise Antarctic cooling over the past 15 million years

PubMed Central

Crampton, James S.; Cody, Rosie D.; Levy, Richard; Harwood, David; McKay, Robert; Naish, Tim R.

2016-01-01

It is not clear how Southern Ocean phytoplankton communities, which form the base of the marine food web and are a crucial element of the carbon cycle, respond to major environmental disturbance. Here, we use a new model ensemble reconstruction of diatom speciation and extinction rates to examine phytoplankton response to climate change in the southern high latitudes over the past 15 My. We identify five major episodes of species turnover (origination rate plus extinction rate) that were coincident with times of cooling in southern high-latitude climate, Antarctic ice sheet growth across the continental shelves, and associated seasonal sea-ice expansion across the Southern Ocean. We infer that past plankton turnover occurred when a warmer-than-present climate was terminated by a major period of glaciation that resulted in loss of open-ocean habitat south of the polar front, driving non-ice adapted diatoms to regional or global extinction. These findings suggest, therefore, that Southern Ocean phytoplankton communities tolerate “baseline” variability on glacial–interglacial timescales but are sensitive to large-scale changes in mean climate state driven by a combination of long-period variations in orbital forcing and atmospheric carbon dioxide perturbations. PMID:27274061

Southern Ocean phytoplankton turnover in response to stepwise Antarctic cooling over the past 15 million years

NASA Astrophysics Data System (ADS)

Crampton, James S.; Cody, Rosie D.; Levy, Richard; Harwood, David; McKay, Robert; Naish, Tim R.

2016-06-01

It is not clear how Southern Ocean phytoplankton communities, which form the base of the marine food web and are a crucial element of the carbon cycle, respond to major environmental disturbance. Here, we use a new model ensemble reconstruction of diatom speciation and extinction rates to examine phytoplankton response to climate change in the southern high latitudes over the past 15 My. We identify five major episodes of species turnover (origination rate plus extinction rate) that were coincident with times of cooling in southern high-latitude climate, Antarctic ice sheet growth across the continental shelves, and associated seasonal sea-ice expansion across the Southern Ocean. We infer that past plankton turnover occurred when a warmer-than-present climate was terminated by a major period of glaciation that resulted in loss of open-ocean habitat south of the polar front, driving non-ice adapted diatoms to regional or global extinction. These findings suggest, therefore, that Southern Ocean phytoplankton communities tolerate “baseline” variability on glacial-interglacial timescales but are sensitive to large-scale changes in mean climate state driven by a combination of long-period variations in orbital forcing and atmospheric carbon dioxide perturbations.

A New Discrete Element Sea-Ice Model for Earth System Modeling

DOE Office of Scientific and Technical Information (OSTI.GOV)

Turner, Adrian Keith

Sea ice forms a frozen crust of sea water oating in high-latitude oceans. It is a critical component of the Earth system because its formation helps to drive the global thermohaline circulation, and its seasonal waxing and waning in the high north and Southern Ocean signi cantly affects planetary albedo. Usually 4{6% of Earth's marine surface is covered by sea ice at any one time, which limits the exchange of heat, momentum, and mass between the atmosphere and ocean in the polar realms. Snow accumulates on sea ice and inhibits its vertical growth, increases its albedo, and contributes to pooledmore » water in melt ponds that darken the Arctic ice surface in the spring. Ice extent and volume are subject to strong seasonal, inter-annual and hemispheric variations, and climatic trends, which Earth System Models (ESMs) are challenged to simulate accurately (Stroeve et al., 2012; Stocker et al., 2013). This is because there are strong coupled feedbacks across the atmosphere-ice-ocean boundary layers, including the ice-albedo feedback, whereby a reduced ice cover leads to increased upper ocean heating, further enhancing sea-ice melt and reducing incident solar radiation re ected back into the atmosphere (Perovich et al., 2008). A reduction in perennial Arctic sea-ice during the satellite era has been implicated in mid-latitude weather changes, including over North America (Overland et al., 2015). Meanwhile, most ESMs have been unable to simulate observed inter-annual variability and trends in Antarctic sea-ice extent during the same period (Gagne et al., 2014).« less

Rising sea levels will reduce extreme temperature variations in tide-dominated reef habitats.

PubMed

Lowe, Ryan Joseph; Pivan, Xavier; Falter, James; Symonds, Graham; Gruber, Renee

2016-08-01

Temperatures within shallow reefs often differ substantially from those in the surrounding ocean; therefore, predicting future patterns of thermal stresses and bleaching at the scale of reefs depends on accurately predicting reef heat budgets. We present a new framework for quantifying how tidal and solar heating cycles interact with reef morphology to control diurnal temperature extremes within shallow, tidally forced reefs. Using data from northwestern Australia, we construct a heat budget model to investigate how frequency differences between the dominant lunar semidiurnal tide and diurnal solar cycle drive ~15-day modulations in diurnal temperature extremes. The model is extended to show how reefs with tidal amplitudes comparable to their depth, relative to mean sea level, tend to experience the largest temperature extremes globally. As a consequence, we reveal how even a modest sea level rise can substantially reduce temperature extremes within tide-dominated reefs, thereby partially offsetting the local effects of future ocean warming.

The dynamics of plate tectonics and mantle flow: from local to global scales.

PubMed

Stadler, Georg; Gurnis, Michael; Burstedde, Carsten; Wilcox, Lucas C; Alisic, Laura; Ghattas, Omar

2010-08-27

Plate tectonics is regulated by driving and resisting forces concentrated at plate boundaries, but observationally constrained high-resolution models of global mantle flow remain a computational challenge. We capitalized on advances in adaptive mesh refinement algorithms on parallel computers to simulate global mantle flow by incorporating plate motions, with individual plate margins resolved down to a scale of 1 kilometer. Back-arc extension and slab rollback are emergent consequences of slab descent in the upper mantle. Cold thermal anomalies within the lower mantle couple into oceanic plates through narrow high-viscosity slabs, altering the velocity of oceanic plates. Viscous dissipation within the bending lithosphere at trenches amounts to approximately 5 to 20% of the total dissipation through the entire lithosphere and mantle.

76 FR 33757 - Ocean Transportation Intermediary License; Applicants

Federal Register 2010, 2011, 2012, 2013, 2014

2011-06-09

... Club Drive, Bensenville, IL 60106. Officers: Dale Jordon, Director (Operations), (Qualifying Individual...), Application Type: Add OFF Service. Oceanic Link USA LLC (NVO & OFF), 5430 Jimmy Carter Blvd., Suite 216... NVO & OFF License. The Ultimate Logistics Service Corporation (NVO & OFF), 3 Birch Place, Pine Brook...

Plankton networks driving carbon export in the oligotrophic ocean

NASA Astrophysics Data System (ADS)

Guidi, L.; Chaffron, S.; Bittner, L.; Eveillard, D.; Raes, J.; Karsenti, E.; Bowler, C.; Gorsky, G.

2016-02-01

The biological carbon pump is the process by which CO2 is transformed to organic carbon via photosynthesis that sinks to the deep ocean as particles where it is sequestered. While the intensity of the pump correlates with plankton community composition, the underlying ecosystem structure and interactions driving the process remain largely uncharacterised. Here we use environmental and metagenomic data gathered during the Tara Oceans expedition to improve our understanding of the underlying processes. We show that specific plankton communities correlate with carbon export and highlight unexpected and overlooked taxa such as Radiolaria, alveolate parasites, as well as Synechococcus and their phages, as lineages most strongly associated with carbon export in the subtropical oligotrophic ocean. Additionally, we show that the relative abundance of just a few bacterial and viral genes can predict most of the variability in carbon export in these regions. Together these results help elucidate ecosystem drivers of the biological carbon pump and present a case study for scaling from genes-to-ecosystems.

Interannual variability of primary production and air-sea CO2 flux in the Atlantic and Indian sectors of the Southern Ocean.

NASA Astrophysics Data System (ADS)

Dufour, Carolina; Merlivat, Liliane; Le Sommer, Julien; Boutin, Jacqueline; Antoine, David

2013-04-01

As one of the major oceanic sinks of anthropogenic CO2, the Southern Ocean plays a critical role in the climate system. However, due to the scarcity of observations, little is known about physical and biological processes that control air-sea CO2 fluxes and how these processes might respond to climate change. It is well established that primary production is one of the major drivers of air-sea CO2 fluxes, consuming surface Dissolved Inorganic Carbon (DIC) during Summer. Southern Ocean primary production is though constrained by several limiting factors such as iron and light availability, which are both sensitive to mixed layer depth. Mixed layer depth is known to be affected by current changes in wind stress or freshwater fluxes over the Southern Ocean. But we still don't know how primary production may respond to anomalous mixed layer depth neither how physical processes may balance this response to set the seasonal cycle of air-sea CO2 fluxes. In this study, we investigate the impact of anomalous mixed layer depth on surface DIC in the Atlantic and Indian sectors of the Subantarctic zone of the Southern Ocean (60W-60E, 38S-55S) with a combination of in situ data, satellite data and model experiment. We use both a regional eddy permitting ocean biogeochemical model simulation based on NEMO-PISCES and data-based reconstruction of biogeochemical fields based on CARIOCA buoys and SeaWiFS data. A decomposition of the physical and biological processes driving the seasonal variability of surface DIC is performed with both the model data and observations. A good agreement is found between the model and the data for the amplitude of biological and air-sea flux contributions. The model data are further used to investigate the impact of winter and summer anomalies in mixed layer depth on surface DIC over the period 1990-2004. The relative changes of each physical and biological process contribution are quantified and discussed.

Nonhydrostatic thermohaline convection in the polar oceans

NASA Astrophysics Data System (ADS)

Potts, Mark Allen

Sea ice cover in the polar and sub-polar seas is an important and sensitive component of the Earth's climate system. It mediates the transfer of heat and momentum between the ocean and the atmosphere in high latitude oceans. Where open patches occur in the ice cover a large transfer of heat from the ocean to the atmosphere occurs that accounts for a large fraction of energy exchange between the wintertime polar ocean and atmosphere. Although the circumstances under which leads and polynyas form are considerably different, similar brine driven convection occurs under both. Convection beneath freezing ice in leads and polynyas can be modeled using either the hydrostatic or nonhydrostatic form of the governing equations. One important question is the degree of nonhydrostaticity, which depends on the vertical accelerations present. This issue is addressed through the application of a nonhydrostatic model, with accurate treatment of the turbulent mixing. The results suggest that mixing and re-freezing considerably modify the fluid dynamical processes underneath, such as the periodic shedding of saline plumes. It also appears that overall, the magnitude of the nonhydrostaticity is small, and hydrostatic models are generally adequate to deal with the problem of convection under leads. Strong wintertime cooling drives deep convection in sub-polar seas and in the coastal waters surrounding Antarctica. Deep convection results in formation of deep water in the global oceans, which is of great importance to the maintenance of the stratification of its deep interior, and the resulting meridional circulation is central to the Earth's climatic state. Deep convection falls into two general categories: open ocean deep convection, which occurs in deep stretches of the high latitude seas far from topographical influences, and convection on or near the continental shelves, where topography exerts a considerable influence. Nonhydrostatic models are central to the study of deep convection, but the presence of the bottom leads to significant complications in shallower waters. This issue of deep convection in the presence of topography is addressed for the first time with a non-hydrostatic model through the adaptation of the virtual boundary method and used to simulate convection over the Mertz Glacier polynya in the Antarctic in both two and three dimensions.

Implementation of methane cycling for deep-time global warming simulations with the DCESS Earth system model (version 1.2)

NASA Astrophysics Data System (ADS)

Shaffer, Gary; Fernández Villanueva, Esteban; Rondanelli, Roberto; Olaf Pepke Pedersen, Jens; Malskær Olsen, Steffen; Huber, Matthew

2017-11-01

Geological records reveal a number of ancient, large and rapid negative excursions of the carbon-13 isotope. Such excursions can only be explained by massive injections of depleted carbon to the Earth system over a short duration. These injections may have forced strong global warming events, sometimes accompanied by mass extinctions such as the Triassic-Jurassic and end-Permian extinctions 201 and 252 million years ago, respectively. In many cases, evidence points to methane as the dominant form of injected carbon, whether as thermogenic methane formed by magma intrusions through overlying carbon-rich sediment or from warming-induced dissociation of methane hydrate, a solid compound of methane and water found in ocean sediments. As a consequence of the ubiquity and importance of methane in major Earth events, Earth system models for addressing such events should include a comprehensive treatment of methane cycling but such a treatment has often been lacking. Here we implement methane cycling in the Danish Center for Earth System Science (DCESS) model, a simplified but well-tested Earth system model of intermediate complexity. We use a generic methane input function that allows variation in input type, size, timescale and ocean-atmosphere partition. To be able to treat such massive inputs more correctly, we extend the model to deal with ocean suboxic/anoxic conditions and with radiative forcing and methane lifetimes appropriate for high atmospheric methane concentrations. With this new model version, we carried out an extensive set of simulations for methane inputs of various sizes, timescales and ocean-atmosphere partitions to probe model behavior. We find that larger methane inputs over shorter timescales with more methane dissolving in the ocean lead to ever-increasing ocean anoxia with consequences for ocean life and global carbon cycling. Greater methane input directly to the atmosphere leads to more warming and, for example, greater carbon dioxide release from land soils. Analysis of synthetic sediment cores from the simulations provides guidelines for the interpretation of real sediment cores spanning the warming events. With this improved DCESS model version and paleo-reconstructions, we are now better armed to gauge the amounts, types, timescales and locations of methane injections driving specific, observed deep-time, global warming events.

Episodic kinematics in continental rifts modulated by changes in mantle melt fraction.

PubMed

Lamb, Simon; Moore, James D P; Smith, Euan; Stern, Tim

2017-07-05

Oceanic crust is created by the extraction of molten rock from underlying mantle at the seafloor 'spreading centres' found between diverging tectonic plates. Modelling studies have suggested that mantle melting can occur through decompression as the mantle flows upwards beneath spreading centres, but direct observation of this process is difficult beneath the oceans. Continental rifts, however-which are also associated with mantle melt production-are amenable to detailed measurements of their short-term kinematics using geodetic techniques. Here we show that such data can provide evidence for an upwelling mantle flow, as well as information on the dimensions and timescale of mantle melting. For North Island, New Zealand, around ten years of campaign and continuous GPS measurements in the continental rift system known as the Taupo volcanic zone reveal that it is extending at a rate of 6-15 millimetres per year. However, a roughly 70-kilometre-long segment of the rift axis is associated with strong horizontal contraction and rapid subsidence, and is flanked by regions of extension and uplift. These features fit a simple model that involves flexure of an elastic upper crust, which is pulled downwards or pushed upwards along the rift axis by a driving force located at a depth greater than 15 kilometres. We propose that flexure is caused by melt-induced episodic changes in the vertical flow forces that are generated by upwelling mantle beneath the rift axis, triggering a transient lower-crustal flow. A drop in the melt fraction owing to melt extraction raises the mantle flow viscosity and drives subsidence, whereas melt accumulation reduces viscosity and allows uplift-processes that are also likely to occur in oceanic spreading centres.

Mechanical Extraction of Power From Ocean Currents and Tides

NASA Technical Reports Server (NTRS)

Jones, Jack; Chao, Yi

2010-01-01

A proposed scheme for generating electric power from rivers and from ocean currents, tides, and waves is intended to offer economic and environmental advantages over prior such schemes, some of which are at various stages of implementation, others of which have not yet advanced beyond the concept stage. This scheme would be less environmentally objectionable than are prior schemes that involve the use of dams to block rivers and tidal flows. This scheme would also not entail the high maintenance costs of other proposed schemes that call for submerged electric generators and cables, which would be subject to degradation by marine growth and corrosion. A basic power-generation system according to the scheme now proposed would not include any submerged electrical equipment. The submerged portion of the system would include an all-mechanical turbine/pump unit that would superficially resemble a large land-based wind turbine (see figure). The turbine axis would turn slowly as it captured energy from the local river flow, ocean current, tidal flow, or flow from an ocean-wave device. The turbine axis would drive a pump through a gearbox to generate an enclosed flow of water, hydraulic fluid, or other suitable fluid at a relatively high pressure [typically approx.500 psi (approx.3.4 MPa)]. The pressurized fluid could be piped to an onshore or offshore facility, above the ocean surface, where it would be used to drive a turbine that, in turn, would drive an electric generator. The fluid could be recirculated between the submerged unit and the power-generation facility in a closed flow system; alternatively, if the fluid were seawater, it could be taken in from the ocean at the submerged turbine/pump unit and discharged back into the ocean from the power-generation facility. Another alternative would be to use the pressurized flow to charge an elevated reservoir or other pumped-storage facility, from whence fluid could later be released to drive a turbine/generator unit at a time of high power demand. Multiple submerged turbine/pump units could be positioned across a channel to extract more power than could be extracted by a single unit. In that case, the pressurized flows in their output pipes would be combined, via check valves, into a wider pipe that would deliver the combined flow to a power-generating or pumped-storage facility.

ENSO Transition Asymmetry: Internal and External Causes and Intermodel Diversity

NASA Astrophysics Data System (ADS)

An, Soon-Il; Kim, Ji-Won

2018-05-01

El Niño is frequently followed by La Niña, but the opposite case rarely happens. Here we explore a mechanism for such an asymmetrical transition and its future changes. Internally, the asymmetrical response of upper ocean waves against surface wind stress anomaly exerts a primary cause of El Niño-Southern Oscillation (ENSO) transition asymmetry. Externally, the asymmetrical capacitor effects of both Indian and Atlantic Oceans play some roles in driving the ENSO transition asymmetry via the interbasin interactions. The historical runs of Coupled Model Intercomparison Project Phase 5 show that the intermodel transition asymmetry is significantly correlated with the intermodel asymmetry in ocean wave response to surface wind forcing but not with that in the interbasin interactions. In addition, the El Niño-to-La Niña transition tendency was weaker in moderate global warming scenario runs (Representative Concentration Pathway 4.5) while slightly enhanced in strong warming scenario runs (Representative Concentration Pathway 8.5). Similar changes also appeared in the asymmetrical response of ocean waves against the surface wind forcing.

3D Visualization of Global Ocean Circulation

NASA Astrophysics Data System (ADS)

Nelson, V. G.; Sharma, R.; Zhang, E.; Schmittner, A.; Jenny, B.

2015-12-01

Advanced 3D visualization techniques are seldom used to explore the dynamic behavior of ocean circulation. Streamlines are an effective method for visualization of flow, and they can be designed to clearly show the dynamic behavior of a fluidic system. We employ vector field editing and extraction software to examine the topology of velocity vector fields generated by a 3D global circulation model coupled to a one-layer atmosphere model simulating preindustrial and last glacial maximum (LGM) conditions. This results in a streamline-based visualization along multiple density isosurfaces on which we visualize points of vertical exchange and the distribution of properties such as temperature and biogeochemical tracers. Previous work involving this model examined the change in the energetics driving overturning circulation and mixing between simulations of LGM and preindustrial conditions. This visualization elucidates the relationship between locations of vertical exchange and mixing, as well as demonstrates the effects of circulation and mixing on the distribution of tracers such as carbon isotopes.

Plate tectonics drive tropical reef biodiversity dynamics

PubMed Central

Leprieur, Fabien; Descombes, Patrice; Gaboriau, Théo; Cowman, Peter F.; Parravicini, Valeriano; Kulbicki, Michel; Melián, Carlos J.; de Santana, Charles N.; Heine, Christian; Mouillot, David; Bellwood, David R.; Pellissier, Loïc

2016-01-01

The Cretaceous breakup of Gondwana strongly modified the global distribution of shallow tropical seas reshaping the geographic configuration of marine basins. However, the links between tropical reef availability, plate tectonic processes and marine biodiversity distribution patterns are still unknown. Here, we show that a spatial diversification model constrained by absolute plate motions for the past 140 million years predicts the emergence and movement of diversity hotspots on tropical reefs. The spatial dynamics of tropical reefs explains marine fauna diversification in the Tethyan Ocean during the Cretaceous and early Cenozoic, and identifies an eastward movement of ancestral marine lineages towards the Indo-Australian Archipelago in the Miocene. A mechanistic model based only on habitat-driven diversification and dispersal yields realistic predictions of current biodiversity patterns for both corals and fishes. As in terrestrial systems, we demonstrate that plate tectonics played a major role in driving tropical marine shallow reef biodiversity dynamics. PMID:27151103

Plate tectonics drive tropical reef biodiversity dynamics.

PubMed

Leprieur, Fabien; Descombes, Patrice; Gaboriau, Théo; Cowman, Peter F; Parravicini, Valeriano; Kulbicki, Michel; Melián, Carlos J; de Santana, Charles N; Heine, Christian; Mouillot, David; Bellwood, David R; Pellissier, Loïc

2016-05-06

The Cretaceous breakup of Gondwana strongly modified the global distribution of shallow tropical seas reshaping the geographic configuration of marine basins. However, the links between tropical reef availability, plate tectonic processes and marine biodiversity distribution patterns are still unknown. Here, we show that a spatial diversification model constrained by absolute plate motions for the past 140 million years predicts the emergence and movement of diversity hotspots on tropical reefs. The spatial dynamics of tropical reefs explains marine fauna diversification in the Tethyan Ocean during the Cretaceous and early Cenozoic, and identifies an eastward movement of ancestral marine lineages towards the Indo-Australian Archipelago in the Miocene. A mechanistic model based only on habitat-driven diversification and dispersal yields realistic predictions of current biodiversity patterns for both corals and fishes. As in terrestrial systems, we demonstrate that plate tectonics played a major role in driving tropical marine shallow reef biodiversity dynamics.

Mean age of oceanic lithosphere drives eustatic sea-level change since Pangea breakup

NASA Astrophysics Data System (ADS)

Cogné, Jean-Pascal; Humler, Eric; Courtillot, Vincent

2006-05-01

The Atlantic and Indian Oceans and the oceanic part of the Antarctic plate have formed at the expense of Panthalassa as a result of Pangea breakup over the last 180 Myr. This major plate reorganization has changed the age vs. surface distribution of oceanic lithosphere and has been a likely driver of sea-level change. Assuming that the age/surface structure of Panthalassa has remained similar to the present-day global distribution from 180 Ma to Present, and using the isochron patterns preserved in the newly formed oceans, we model resulting relative sea-level change. We find a first (slower) phase of sea-level rise (by 90 to 110 m), culminating between 120 and 50 Ma, followed by a (faster) phase of sea-level drop. We show that this result is not strongly sensitive to our hypothesis of constant mean age of Panthalassa, for which much of the information is now erased due to subduction. When the effects of oceanic plateau formation and ice cap development are added, the predicted sea-level curve fits remarkably well the first-order variations of observed sea-level change. We conclude that the changes in mean age of the oceanic lithosphere (varying between 56 and 62 ± 0.2 Myr), which are simply the expression of the Wilson cycle following Pangea breakup, are the main control, accounting for ˜ 70%, of first-order changes in sea-level.

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2012-08-16

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Relationship Between Sea Surface Temperature and Surface Heat Balance Trends in the Tropical Oceans: The Crucial Role of Surface Wind Trends

NASA Astrophysics Data System (ADS)

Cook, K. H.; Vizy, E. K.; Sun, X.

2016-12-01

Multiple atmospheric and ocean reanalyses are analyzed for 1980-2015 to understand annual-mean adjustments of the surface heat balance over the tropical oceans as the climate warms. Linear trends are examined, with statistical significance evaluated. While surface heat budgets and sea surface temperatures are mutually adjusted fields, insights into the physical processes of this adjustment and the implications for temperature trends can be identified. Two second-generation reanalyses, ERA-Interim and JRA-55, agree well on the distributions and magnitudes of trends in the net heat flux from the atmosphere to the ocean. Trends in the net longwave and sensible heat fluxes are generally small, and trends in solar radiation absorbed are only influential regionally and vary among the reanalyses. The largest contribution is from latent heat flux trends. Contributions to these trends associated with surface temperature (thermal-driving), 10-m wind (dynamical-driving) and specific humidity (hydrological-driving) trends are estimated. The dynamically-driven latent heat flux dominates and explains much of the regionality of the multi-decadal heat flux trends. However, trends in the net surface heat flux alone do not match the observed SSTs trends well, indicating that the redistribution of heat within the ocean mixed layer is also important. Ocean mixed layer heat budgets in various ocean reanalyses are examined to understand this redistribution, and we again identify a crucial role for changes in the surface wind. Acceleration of the tropical easterlies is associated with strengthening of the equatorial undercurrents in both the tropical Pacific and Atlantic. In the Pacific, where the EUC is also shoaling, the result is enhanced warm-water advection into the central Pacific. This advective warming is superimposed on cooling due to enhanced evaporation and equatorial upwelling, which are also associated with wind trends, to determine the observed pattern of SST trends.

The Importance of Submesoscale Versus Basin-scale Processes in Driving the Subpolar Spring Phytoplankton Bloom.

NASA Astrophysics Data System (ADS)

Brody, S.; Mahadevan, A.; Lozier, M. S.

2014-12-01

The subpolar spring phytoplankton bloom has important consequences for marine ecosystems and the carbon cycle. The timing of the bloom has been conceived of as a basin-scale event: as the ocean warms, the seasonal mixed layer shoals, restricting phytoplankton to shallower depths and increasing available light to a level at which the bloom can begin. Recent studies have highlighted the importance of localized phenomena in driving the bloom initiation. Specifically, the role of lateral density gradients in generating <10km instabilities in the upper ocean, which then stratify the mixed layer before surface heating begins, has been explored with a process study model and fine-scale observations from a field program to study the North Atlantic spring bloom [1]. However, an alternative hypothesis has recently been validated at both the small scale, using the same observational data [2], and at the basin scale, using remote sensing data [3]. According to this hypothesis, blooms begin when surface heat fluxes weaken, mixing shifts from primarily convectively-driven to primarily wind-driven, and the depth of active mixing in the upper ocean consequently decreases. Here, we compare the importance of the barriers to mixing presented by submesoscale instabilities with the decreases in mixing depth caused by changes in surface forcing in driving the initiation of the spring bloom prior to the onset of surface heating. To make this comparison, we use a Lagrangian framework to track the light history of particles seeded in a high-resolution numerical model that we initialize with various surface forcing scenarios, and with and without lateral density gradients. Because the model parameterizes convection with convective adjustment, we present two methodologies to account for turbulent mixing processes that utilize observations of turbulent vertical mixing from a Lagrangian float. We present conclusions on whether and how submesoscale processes affect bloom initiation under varied surface forcing conditions in the context of whether the timing of the subpolar phytoplankton bloom can be thought of as a basin-scale or submesoscale phenomenon. [1] A. Mahadevan et al.. Science 337, 6090 (2012). [2] Brody, S.R. and Lozier, M.S. (under review, ICES J. Mar. Sci) [3] Brody, S.R. and Lozier, M.S. Geophys. Res. Lett. 41, (2014).

Madagascar's escape from Africa: A high-resolution plate reconstruction for the Western Somali Basin and implications for supercontinent dispersal

NASA Astrophysics Data System (ADS)

Phethean, Jordan J. J.; Kalnins, Lara M.; van Hunen, Jeroen; Biffi, Paolo G.; Davies, Richard J.; McCaffrey, Ken J. W.

2016-12-01

Accurate reconstructions of the dispersal of supercontinent blocks are essential for testing continental breakup models. Here, we provide a new plate tectonic reconstruction of the opening of the Western Somali Basin during the breakup of East and West Gondwana. The model is constrained by a new comprehensive set of spreading lineaments, detected in this heavily sedimented basin using a novel technique based on directional derivatives of free-air gravity anomalies. Vertical gravity gradient and free-air gravity anomaly maps also enable the detection of extinct mid-ocean ridge segments, which can be directly compared to several previous ocean magnetic anomaly interpretations of the Western Somali Basin. The best matching interpretations have basin symmetry around the M0 anomaly; these are then used to temporally constrain our plate tectonic reconstruction. The reconstruction supports a tight fit for Gondwana fragments prior to breakup, and predicts that the continent-ocean transform margin lies along the Rovuma Basin, not along the Davie Fracture Zone (DFZ) as commonly thought. According to our reconstruction, the DFZ represents a major ocean-ocean fracture zone formed by the coalescence of several smaller fracture zones during evolving plate motions as Madagascar drifted southwards, and offshore Tanzania is an obliquely rifted, rather than transform, margin. New seismic reflection evidence for oceanic crust inboard of the DFZ strongly supports these conclusions. Our results provide important new constraints on the still enigmatic driving mechanism of continental rifting, the nature of the lithosphere in the Western Somali Basin, and its resource potential.

The response of an ocean general circulation model to surface wind stress produced by an atmospheric general circulation model

DOE Office of Scientific and Technical Information (OSTI.GOV)

Huang, B.; Schneider, E.K.

1995-10-01

Two surface wind stress datasets for 1979-91, one based on observations and the other from an investigation of the COLA atmospheric general circulation model (AGCM) with prescribed SST, are used to drive the GFDL ocean general circulation model. These two runs are referred to as the control and COLA experiments, respectively. Simulated SST and upper-ocean heat contents (HC) in the tropical Pacific Ocean are compared with observations and between experiments. Both simulation reproduced the observed mean SST and HC fields as well as their annual cycles realistically. Major errors common to both runs are colder than observed SST in themore » eastern equatorial ocean and HC in the western Pacific south of the equator, with errors generally larger in the COLA experiment. New errors arising from the AGCM wind forcing include higher SST near the South American coast throughout the year and weaker HC gradients along the equator in boreal spring. The former is associated with suppressed coastal upwelling by weak along shore AGCM winds, and the latter is caused by weaker equatorial easterlies in boreal spring. The low-frequency ENSO fluctuations are also realistic for both runs. Correlations between the observed and simulated SST anomalies from the COLA simulation are as high as those from the control run in the central equatorial Pacific. A major problem in the COLA simulation is the appearance of unrealistic tropical cold anomalies during the boreal spring of mature El Nino years. These anomalies propagate along the equator from the western Pacific to the eastern coast in about three months, and temporarily eliminate the warm SST and HC anomalies in the eastern Pacific. This erroneous oceanic response in the COLA simulation is caused by a reversal of the westerly wind anomalies on the equator, associated with an unrealistic southward shift of the ITCZ in boreal spring during El Nino events. 66 refs., 16 figs.« less

Climate change and the oceans--what does the future hold?

PubMed

Bijma, Jelle; Pörtner, Hans-O; Yesson, Chris; Rogers, Alex D

2013-09-30

The ocean has been shielding the earth from the worst effects of rapid climate change by absorbing excess carbon dioxide from the atmosphere. This absorption of CO2 is driving the ocean along the pH gradient towards more acidic conditions. At the same time ocean warming is having pronounced impacts on the composition, structure and functions of marine ecosystems. Warming, freshening (in some areas) and associated stratification are driving a trend in ocean deoxygenation, which is being enhanced in parts of the coastal zone by upwelling of hypoxic deep water. The combined impact of warming, acidification and deoxygenation are already having a dramatic effect on the flora and fauna of the oceans with significant changes in distribution of populations, and decline of sensitive species. In many cases, the impacts of warming, acidification and deoxygenation are increased by the effects of other human impacts, such as pollution, eutrophication and overfishing. The interactive effects of this deadly trio mirrors similar events in the Earth's past, which were often coupled with extinctions of major species' groups. Here we review the observed impacts and, using past episodes in the Earth's history, set out what the future may hold if carbon emissions and climate change are not significantly reduced with more or less immediate effect. Copyright © 2013. Published by Elsevier Ltd.

Tropically driven and externally forced patterns of Antarctic sea ice change: reconciling observed and modeled trends

NASA Astrophysics Data System (ADS)

Schneider, David P.; Deser, Clara

2018-06-01

Recent work suggests that natural variability has played a significant role in the increase of Antarctic sea ice extent during 1979-2013. The ice extent has responded strongly to atmospheric circulation changes, including a deepened Amundsen Sea Low (ASL), which in part has been driven by tropical variability. Nonetheless, this increase has occurred in the context of externally forced climate change, and it has been difficult to reconcile observed and modeled Antarctic sea ice trends. To understand observed-model disparities, this work defines the internally driven and radiatively forced patterns of Antarctic sea ice change and exposes potential model biases using results from two sets of historical experiments of a coupled climate model compared with observations. One ensemble is constrained only by external factors such as greenhouse gases and stratospheric ozone, while the other explicitly accounts for the influence of tropical variability by specifying observed SST anomalies in the eastern tropical Pacific. The latter experiment reproduces the deepening of the ASL, which drives an increase in regional ice extent due to enhanced ice motion and sea surface cooling. However, the overall sea ice trend in every ensemble member of both experiments is characterized by ice loss and is dominated by the forced pattern, as given by the ensemble-mean of the first experiment. This pervasive ice loss is associated with a strong warming of the ocean mixed layer, suggesting that the ocean model does not locally store or export anomalous heat efficiently enough to maintain a surface environment conducive to sea ice expansion. The pervasive upper-ocean warming, not seen in observations, likely reflects ocean mean-state biases.

Tropically driven and externally forced patterns of Antarctic sea ice change: reconciling observed and modeled trends

NASA Astrophysics Data System (ADS)

Schneider, David P.; Deser, Clara

2017-09-01

Recent work suggests that natural variability has played a significant role in the increase of Antarctic sea ice extent during 1979-2013. The ice extent has responded strongly to atmospheric circulation changes, including a deepened Amundsen Sea Low (ASL), which in part has been driven by tropical variability. Nonetheless, this increase has occurred in the context of externally forced climate change, and it has been difficult to reconcile observed and modeled Antarctic sea ice trends. To understand observed-model disparities, this work defines the internally driven and radiatively forced patterns of Antarctic sea ice change and exposes potential model biases using results from two sets of historical experiments of a coupled climate model compared with observations. One ensemble is constrained only by external factors such as greenhouse gases and stratospheric ozone, while the other explicitly accounts for the influence of tropical variability by specifying observed SST anomalies in the eastern tropical Pacific. The latter experiment reproduces the deepening of the ASL, which drives an increase in regional ice extent due to enhanced ice motion and sea surface cooling. However, the overall sea ice trend in every ensemble member of both experiments is characterized by ice loss and is dominated by the forced pattern, as given by the ensemble-mean of the first experiment. This pervasive ice loss is associated with a strong warming of the ocean mixed layer, suggesting that the ocean model does not locally store or export anomalous heat efficiently enough to maintain a surface environment conducive to sea ice expansion. The pervasive upper-ocean warming, not seen in observations, likely reflects ocean mean-state biases.

Sustained climate warming drives declining marine biological productivity

DOE PAGES

Moore, J. Keith; Fu, Weiwei; Primeau, Francois; ...

2018-03-01

Climate change projections to the year 2100 may miss physical-biogeochemical feedbacks that emerge later from the cumulative effects of climate warming. In a coupled climate simulation to the year 2300, the westerly winds strengthen and shift poleward, surface waters warm, and sea ice disappears, leading to intense nutrient trapping in the Southern Ocean. The trapping drives a global-scale nutrient redistribution, with net transfer to the deep ocean. Ensuing surface nutrient reductions north of 30°S drive steady declines in primary production and carbon export (decreases of 24 and 41%, respectively, by 2300). Potential fishery yields, constrained by lower–trophic-level productivity, decrease bymore » more than 20% globally and by nearly 60% in the North Atlantic. Continued high levels of greenhouse gas emissions could suppress marine biological productivity for a millennium.« less

Sustained climate warming drives declining marine biological productivity

DOE Office of Scientific and Technical Information (OSTI.GOV)

Moore, J. Keith; Fu, Weiwei; Primeau, Francois

Climate change projections to the year 2100 may miss physical-biogeochemical feedbacks that emerge later from the cumulative effects of climate warming. In a coupled climate simulation to the year 2300, the westerly winds strengthen and shift poleward, surface waters warm, and sea ice disappears, leading to intense nutrient trapping in the Southern Ocean. The trapping drives a global-scale nutrient redistribution, with net transfer to the deep ocean. Ensuing surface nutrient reductions north of 30°S drive steady declines in primary production and carbon export (decreases of 24 and 41%, respectively, by 2300). Potential fishery yields, constrained by lower–trophic-level productivity, decrease bymore » more than 20% globally and by nearly 60% in the North Atlantic. Continued high levels of greenhouse gas emissions could suppress marine biological productivity for a millennium.« less

77 FR 70162 - Ocean Transportation Intermediary License Applicants

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2012-11-23

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2013-04-10

...), Application Type: QI Change. Morgan USA Logistics Inc (NVO), 16 Birchwood Park Drive, Syosset, NY 11791... Hull Logistics, LLC (NVO & OFF), 17890 Cedarwood Drive, Riverside, CA 92803, Officers: Stanley J... Baines, Chairman of the Board, Application Type: New NVO & OFF License. Point Global Logistics, LLC (OFF...

Coastal ocean and shelf-sea biogeochemical cycling of trace elements and isotopes: lessons learned from GEOTRACES

PubMed Central

Lam, Phoebe J.; Lohan, Maeve C.; Kwon, Eun Young; Hatje, Vanessa; Shiller, Alan M.; Cutter, Gregory A.; Thomas, Alex; Milne, Angela; Thomas, Helmuth; Andersson, Per S.; Porcelli, Don; Tanaka, Takahiro; Geibert, Walter; Dehairs, Frank; Garcia-Orellana, Jordi

2016-01-01

Continental shelves and shelf seas play a central role in the global carbon cycle. However, their importance with respect to trace element and isotope (TEI) inputs to ocean basins is less well understood. Here, we present major findings on shelf TEI biogeochemistry from the GEOTRACES programme as well as a proof of concept for a new method to estimate shelf TEI fluxes. The case studies focus on advances in our understanding of TEI cycling in the Arctic, transformations within a major river estuary (Amazon), shelf sediment micronutrient fluxes and basin-scale estimates of submarine groundwater discharge. The proposed shelf flux tracer is 228-radium (T1/2 = 5.75 yr), which is continuously supplied to the shelf from coastal aquifers, sediment porewater exchange and rivers. Model-derived shelf 228Ra fluxes are combined with TEI/ 228Ra ratios to quantify ocean TEI fluxes from the western North Atlantic margin. The results from this new approach agree well with previous estimates for shelf Co, Fe, Mn and Zn inputs and exceed published estimates of atmospheric deposition by factors of approximately 3–23. Lastly, recommendations are made for additional GEOTRACES process studies and coastal margin-focused section cruises that will help refine the model and provide better insight on the mechanisms driving shelf-derived TEI fluxes to the ocean. This article is part of the themed issue ‘Biological and climatic impacts of ocean trace element chemistry’. PMID:29035267

Coastal ocean and shelf-sea biogeochemical cycling of trace elements and isotopes: lessons learned from GEOTRACES

NASA Astrophysics Data System (ADS)

Charette, Matthew A.; Lam, Phoebe J.; Lohan, Maeve C.; Kwon, Eun Young; Hatje, Vanessa; Jeandel, Catherine; Shiller, Alan M.; Cutter, Gregory A.; Thomas, Alex; Boyd, Philip W.; Homoky, William B.; Milne, Angela; Thomas, Helmuth; Andersson, Per S.; Porcelli, Don; Tanaka, Takahiro; Geibert, Walter; Dehairs, Frank; Garcia-Orellana, Jordi

2016-11-01

Continental shelves and shelf seas play a central role in the global carbon cycle. However, their importance with respect to trace element and isotope (TEI) inputs to ocean basins is less well understood. Here, we present major findings on shelf TEI biogeochemistry from the GEOTRACES programme as well as a proof of concept for a new method to estimate shelf TEI fluxes. The case studies focus on advances in our understanding of TEI cycling in the Arctic, transformations within a major river estuary (Amazon), shelf sediment micronutrient fluxes and basin-scale estimates of submarine groundwater discharge. The proposed shelf flux tracer is 228-radium (T1/2 = 5.75 yr), which is continuously supplied to the shelf from coastal aquifers, sediment porewater exchange and rivers. Model-derived shelf 228Ra fluxes are combined with TEI/ 228Ra ratios to quantify ocean TEI fluxes from the western North Atlantic margin. The results from this new approach agree well with previous estimates for shelf Co, Fe, Mn and Zn inputs and exceed published estimates of atmospheric deposition by factors of approximately 3-23. Lastly, recommendations are made for additional GEOTRACES process studies and coastal margin-focused section cruises that will help refine the model and provide better insight on the mechanisms driving shelf-derived TEI fluxes to the ocean. This article is part of the themed issue 'Biological and climatic impacts of ocean trace element chemistry'.

Coastal ocean and shelf-sea biogeochemical cycling of trace elements and isotopes: lessons learned from GEOTRACES.

PubMed

Charette, Matthew A; Lam, Phoebe J; Lohan, Maeve C; Kwon, Eun Young; Hatje, Vanessa; Jeandel, Catherine; Shiller, Alan M; Cutter, Gregory A; Thomas, Alex; Boyd, Philip W; Homoky, William B; Milne, Angela; Thomas, Helmuth; Andersson, Per S; Porcelli, Don; Tanaka, Takahiro; Geibert, Walter; Dehairs, Frank; Garcia-Orellana, Jordi

2016-11-28

Continental shelves and shelf seas play a central role in the global carbon cycle. However, their importance with respect to trace element and isotope (TEI) inputs to ocean basins is less well understood. Here, we present major findings on shelf TEI biogeochemistry from the GEOTRACES programme as well as a proof of concept for a new method to estimate shelf TEI fluxes. The case studies focus on advances in our understanding of TEI cycling in the Arctic, transformations within a major river estuary (Amazon), shelf sediment micronutrient fluxes and basin-scale estimates of submarine groundwater discharge. The proposed shelf flux tracer is 228-radium ( T 1/2  = 5.75 yr), which is continuously supplied to the shelf from coastal aquifers, sediment porewater exchange and rivers. Model-derived shelf 228 Ra fluxes are combined with TEI/ 228 Ra ratios to quantify ocean TEI fluxes from the western North Atlantic margin. The results from this new approach agree well with previous estimates for shelf Co, Fe, Mn and Zn inputs and exceed published estimates of atmospheric deposition by factors of approximately 3-23. Lastly, recommendations are made for additional GEOTRACES process studies and coastal margin-focused section cruises that will help refine the model and provide better insight on the mechanisms driving shelf-derived TEI fluxes to the ocean.This article is part of the themed issue 'Biological and climatic impacts of ocean trace element chemistry'. © 2015 The Authors.

Importance of dispersal routes that minimize open-ocean movement to the genetic structure of island populations.

PubMed

Harradine, E L; Andrew, M E; Thomas, J W; How, R A; Schmitt, L H; Spencer, P B S

2015-12-01

Islands present a unique scenario in conservation biology, offering refuge yet imposing limitations on insular populations. The Kimberley region of northwestern Australia has more than 2500 islands that have recently come into focus as substantial conservation resources. It is therefore of great interest for managers to understand the driving forces of genetic structure of species within these island archipelagos. We used the ubiquitous bar-shouldered skink (Ctenotus inornatus) as a model species to represent the influence of landscape factors on genetic structure across the Kimberley islands. On 41 islands and 4 mainland locations in a remote area of Australia, we genotyped individuals across 18 nuclear (microsatellite) markers. Measures of genetic differentiation and diversity were used in two complementary analyses. We used circuit theory and Mantel tests to examine the influence of the landscape matrix on population connectivity and linear regression and model selection based on Akaike's information criterion to investigate landscape controls on genetic diversity. Genetic differentiation between islands was best predicted with circuit-theory models that accounted for the large difference in resistance to dispersal between land and ocean. In contrast, straight-line distances were unrelated to either resistance distances or genetic differentiation. Instead, connectivity was determined by island-hopping routes that allow organisms to minimize the distance of difficult ocean passages. Island populations of C. inornatus retained varying degrees of genetic diversity (NA = 1.83 - 7.39), but it was greatest on islands closer to the mainland, in terms of resistance-distance units. In contrast, genetic diversity was unrelated to island size. Our results highlight the potential for islands to contribute to both theoretical and applied conservation, provide strong evidence of the driving forces of population structure within undisturbed landscapes, and identify the islands most valuable for conservation based on their contributions to gene flow and genetic diversity. © 2015 Society for Conservation Biology.

Reconstruction of the Eemian climate using a fully coupled Earth system model

NASA Astrophysics Data System (ADS)

Rybak, Oleg; Volodin, Evgeny; Morozova, Polina; Huybrechts, Philippe

2017-04-01

Climate of the Last Interglacial (LIG) between ca. 130 and 115 kyr BP is thought to be a good analogue for future climate warming. Though the driving mechanisms of the past and current climate evolution differ, analysis of the LIG climate may provide important insights for projections of future environmental changes. We do not know properly what was spatial distribution and magnitude of surface air temperature and precipitation anomalies with respect to present. Sparse proxy data are attributed mostly to the continental margins, internal areas of ice sheets and particular regions of the World Ocean. Combining mathematical modeling and indirect evidence can help to identify driving mechanisms and feed-backs which formed climatic conditions of the LIG. In order to reproduce the LIG climate, we carried out transient numerical experiments using a fully coupled Earth System Model (ESM) consisting of an AO GCM, which includes decription of the biosphere, atmospheric and oceanic chemistry ets. (INMCM), developed in the Institute of Numerical Mathematics (Moscow, Russia) and the models of Greenland and Antarctic ice sheets (GrISM and AISM, Vrije Uninersiteit Brussel, Belgium). Though the newest version of the INMCM has rather high spatial resolution, it canot be used in long transient numerical experimemts because of high computational demand. Coupling of the GrISM and AISM to the low resolution version of the INMCM is complicated by essential differences in spatial and temporal scales of cryospheric, atmosphere and the ocean components of the ESM (spatial resolution 5˚×4˚, 21 vertical layers in the atmospheric block, 2.5°×2°, 6 min. temporal resolution; 33 vertical layers in the oceanic block; 20×20 km, 51 vertical layers and 1 yr temporal resolution in the GrISM and AISM). We apply two different coupling strategies. AISM is incorporated into the ESM via using procedures of resampling and interpolation of the input fields of annually averaged air surface temperatures and precipitation fields generated by the INMCM. To provide interactive coupling of the INMCM and the GrISM, we employ a special energy- and water balance model (EWBM-G), which serves as a buffer providing effective data exchange between sub-models. EWBM-G operates in a rectangle domain including Greenland and calculates annual surface mass balance (further transferred as an external forcing to the GrISM) and fresh water flux (transferred to the oceanic block of the INMCM). Orbital parameters of the LIG were set with 1 kyr step with further interpolation to 100 years. Assuming concentrations of greenhouse gases during the LIG were not very much different from the preindustrial values, this potential forcing was neglected. Climatic block of the ESM was called every 100 model years to follow changes in orbital forcing. AISM and GrISM were asynchronously coupled to sub-models of the atmosphere and the ocean with the ratio of model years as 100 to 1. Obtained fields of deviations of air surface temperature from preindustrial values correspond in general to the estimates made in earlier studies. Evaluated contribution of the Greenland ice sheet to the global sea level rise (approximately 2 m) supports the newest estimates based on model results and proxy data analysis.

77 FR 30022 - U.S. Extractive Industries Transparency Initiative Stakeholder Assessment Public Listening...

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... maintain a valid bond. LICENSE NUMBER: 4373F. NAME: Elite Airfreight, Inc. ADDRESS: 16303 Air Center Blvd...: 16283N. NAME: Sea Air Surface Distribution, Inc. ADDRESS: 2018 Mount Forest Drive, Kingwood, TX 78521... 26, 2010. REASON: Failed to maintain a valid bond. LICENSE NUMBER: 18012F. NAME: Speedex Air & Ocean...

77 FR 38288 - Ocean Transportation Intermediary License; Applicants

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...). Application Type: Name Change. Global Atlantic Logistics LLC (OFF), 1901 SW 31st Avenue, Pembroke Park, FL....gov . Bellcom, Inc. (NVO), 503 Commerce Park Drive, Suite E, Marietta, GA 30060. Officers: Cornelius U... License. Benchmark Worldwide Logistics, Inc. dba Star Ocean Lines (NVO & OFF), 24900 South Route 53...

75 FR 42446 - Ocean Transportation Intermediary License Applicants

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... Change. CACC Global Logistics, Inc. (NVO & OFF), 151 E. 220th Street, Carson, CA 90754. Officers: Annie... NVO & OFF License. E-Freight Solutions Inc. dba E-Lines Shipping and Logistics, and Ocean Champ Shipping Limited (NVO), 1000 Corporate Center Drive, Suite 320, Monterey Park, CA 91754. Officers: Joey Tam...

Dynamics of the global meridional ice flow of Europa's icy shell

NASA Astrophysics Data System (ADS)

Ashkenazy, Yosef; Sayag, Roiy; Tziperman, Eli

2018-01-01

Europa is one of the most probable places in the solar system to find extra-terrestrial life1,2, motivating the study of its deep ( 100 km) ocean3-6 and thick icy shell3,7-11. The chaotic terrain patterns on Europa's surface12-15 have been associated with vertical convective motions within the ice8,10. Horizontal gradients of ice thickness16,17 are expected due to the large equator-to-pole gradient of surface temperature and can drive a global horizontal ice flow, yet such a flow and its observable implications have not been studied. We present a global ice flow model for Europa composed of warm, soft ice flowing beneath a cold brittle rigid ice crust3. The model is coupled to an underlying (diffusive) ocean and includes the effect of tidal heating and convection within the ice. We show that Europa's ice can flow meridionally due to pressure gradients associated with equator-to-pole ice thickness differences, which can be up to a few km and can be reduced both by ice flow and due to ocean heat transport. The ice thickness and meridional flow direction depend on whether the ice convects or not; multiple (convecting and non-convecting) equilibria are found. Measurements of the ice thickness and surface temperature from future Europa missions18,19 can be used with our model to deduce whether Europa's icy shell convects and to constrain the effectiveness of ocean heat transport.

Time-slice analysis of the Australian summer monsoon during the late Quaternary using the Fast Ocean Atmosphere Model

NASA Astrophysics Data System (ADS)

Marshall, A. G.; Lynch, A. H.

2006-10-01

We use the Fast Ocean Atmosphere Model (FOAM) to investigate the variation in the Australian summer monsoon over the last 55 000 years. A synthesis of palaeoenvironmental observations is used to constrain the model for six time slices: 55, 35, 21, 11, 6 and 0 ka. Both inter-hemispheric forcing and the seasonal timing of local insolation changes play key, and interacting, roles on the evolution and intensity of the monsoon.During the onset to the monsoon, a heat low develops to the west of Australia over the Indian Ocean in all time slices, but with varying strengths. Divergent outflow from Asia converges with the cyclonic flow to bring increased rainfall to northern Australia and the maritime continent. The relative importance of a low pressure pull and the high pressure push varies according to the strength of the pressure anomalies. Only in the middle Holocene is the low pressure pull the dominant forcing mechanism. At 21 ka, the climate shift to colder mean temperatures determines the large-scale dynamics of the monsoon.The general picture that emerges from these results is consistent with available palaeodata but highlights the importance of a broad regional perspective to ascribe the driving mechanisms at different times. Copyright

Wave-current interaction: Effect on the wave field in a semi-enclosed basin

NASA Astrophysics Data System (ADS)

Benetazzo, A.; Carniel, S.; Sclavo, M.; Bergamasco, A.

2013-10-01

The effect on waves of the Wave-Current Interaction (WCI) process in the semi-enclosed Gulf of Venice (northern region of the Adriatic Sea) was investigated using the Coupled Ocean-Atmosphere-Wave-Sediment Transport (COAWST) modeling system. COAWST relies on the ocean model ROMS (Regional Ocean Modeling System), the wave model SWAN (Simulating WAves Nearshore), and the CSTMS (Community Sediment Transport Modeling System) routines. The two-way data transfer between circulation and wave models was synchronous via MCT (Model Coupling Toolkit), with ROMS providing: current field, free surface elevation, and bathymetry to SWAN. For coupling, the 3-D current profiles were averaged using a formulation which integrated the near-surface velocity over a depth controlled by the spectral mean wavenumber. COAWST system was implemented on a parent grid (with horizontal resolution of 2.0 km) covering the whole Adriatic Sea with one-way nesting to a child grid resolving the northern area (Gulf of Venice) at a resolution of 0.5 km. The meteorological forcings provided by the operational meteorological model COSMO-I7 (a mesoscale model developed in the framework of the COSMO Consortium) were used to drive the modeling system in the period bracketing September 2010-August 2011. The adopted winds and the simulated waves were compared with observations at the CNR-ISMAR Acqua Alta oceanographic tower, located off the Venice littoral. Wave heights and sea surface winds were also compared with satellite-derived data. The analysis of WCI was performed on the child grid over the winter season (January-March 2011) with particular focus on the waves generated by prevailing and dominant winds blowing on the Adriatic Sea: Bora and Sirocco. Due to the variable wind direction with respect to the ocean current direction different effects on WCI were depicted, showing that within the northern Adriatic Sea the ocean-wave interactions are strongly dependent on the wind forcing direction. Further investigations reveal that, when applied to intense storms, the effect of coupling on waves results in variations of significant wave height up to 0.6 m, with some areas experiencing significant increase/decrease of wave spectral energy for opposite/following currents respectively.

Functional group-specific traits drive phytoplankton dynamics in the oligotrophic ocean.

PubMed

Alexander, Harriet; Rouco, Mónica; Haley, Sheean T; Wilson, Samuel T; Karl, David M; Dyhrman, Sonya T

2015-11-03

A diverse microbial assemblage in the ocean is responsible for nearly half of global primary production. It has been hypothesized and experimentally demonstrated that nutrient loading can stimulate blooms of large eukaryotic phytoplankton in oligotrophic systems. Although central to balancing biogeochemical models, knowledge of the metabolic traits that govern the dynamics of these bloom-forming phytoplankton is limited. We used eukaryotic metatranscriptomic techniques to identify the metabolic basis of functional group-specific traits that may drive the shift between net heterotrophy and autotrophy in the oligotrophic ocean. Replicated blooms were simulated by deep seawater (DSW) addition to mimic nutrient loading in the North Pacific Subtropical Gyre, and the transcriptional responses of phytoplankton functional groups were assayed. Responses of the diatom, haptophyte, and dinoflagellate functional groups in simulated blooms were unique, with diatoms and haptophytes significantly (95% confidence) shifting their quantitative metabolic fingerprint from the in situ condition, whereas dinoflagellates showed little response. Significantly differentially abundant genes identified the importance of colimitation by nutrients, metals, and vitamins in eukaryotic phytoplankton metabolism and bloom formation in this system. The variable transcript allocation ratio, used to quantify transcript reallocation following DSW amendment, differed for diatoms and haptophytes, reflecting the long-standing paradigm of phytoplankton r- and K-type growth strategies. Although the underlying metabolic potential of the large eukaryotic phytoplankton was consistently present, the lack of a bloom during the study period suggests a crucial dependence on physical and biogeochemical forcing, which are susceptible to alteration with changing climate.

Functional group-specific traits drive phytoplankton dynamics in the oligotrophic ocean

PubMed Central

Alexander, Harriet; Rouco, Mónica; Haley, Sheean T.; Wilson, Samuel T.; Karl, David M.; Dyhrman, Sonya T.

2015-01-01

A diverse microbial assemblage in the ocean is responsible for nearly half of global primary production. It has been hypothesized and experimentally demonstrated that nutrient loading can stimulate blooms of large eukaryotic phytoplankton in oligotrophic systems. Although central to balancing biogeochemical models, knowledge of the metabolic traits that govern the dynamics of these bloom-forming phytoplankton is limited. We used eukaryotic metatranscriptomic techniques to identify the metabolic basis of functional group-specific traits that may drive the shift between net heterotrophy and autotrophy in the oligotrophic ocean. Replicated blooms were simulated by deep seawater (DSW) addition to mimic nutrient loading in the North Pacific Subtropical Gyre, and the transcriptional responses of phytoplankton functional groups were assayed. Responses of the diatom, haptophyte, and dinoflagellate functional groups in simulated blooms were unique, with diatoms and haptophytes significantly (95% confidence) shifting their quantitative metabolic fingerprint from the in situ condition, whereas dinoflagellates showed little response. Significantly differentially abundant genes identified the importance of colimitation by nutrients, metals, and vitamins in eukaryotic phytoplankton metabolism and bloom formation in this system. The variable transcript allocation ratio, used to quantify transcript reallocation following DSW amendment, differed for diatoms and haptophytes, reflecting the long-standing paradigm of phytoplankton r- and K-type growth strategies. Although the underlying metabolic potential of the large eukaryotic phytoplankton was consistently present, the lack of a bloom during the study period suggests a crucial dependence on physical and biogeochemical forcing, which are susceptible to alteration with changing climate. PMID:26460011

77 FR 65887 - Ocean Transportation Intermediary License Applicants

Federal Register 2010, 2011, 2012, 2013, 2014

2012-10-31

..., Washington, DC 20573, by telephone at (202) 523-5843 or by email at [email protected] . ACM Logistics & Consulting... Type: New OFF License; Highland Project Logistics, Inc. (NVO & OFF), 35 Constitution Drive, Suite A...: New NVO License; Koch Maritime, Inc (NVO & OFF), 2230 Energy Park Drive, St. Paul, MN 55108, Officers...

75 FR 65017 - Ocean Transportation Intermediary License Revocations

Federal Register 2010, 2011, 2012, 2013, 2014

2010-10-21

...: 6701 Moravia Park Drive, Unit B, Baltimore, MD 21237. Date Revoked: September 17, 2010. Reason: Failed.... License Number: 018717N. Name: IFE Global Logistics Inc. Address: 100 North Hill Drive, 16, Brisbane, CA... Logistics Inc. Address: 1001 Nicholas Blvd., A, Elk Grove Village, IL 60007. Date Revoked: September 10...

Processes of 30-90 days sea surface temperature variability in the northern Indian Ocean during boreal summer

NASA Astrophysics Data System (ADS)

Vialard, J.; Jayakumar, A.; Gnanaseelan, C.; Lengaigne, M.; Sengupta, D.; Goswami, B. N.

2012-05-01

During summer, the northern Indian Ocean exhibits significant atmospheric intraseasonal variability associated with active and break phases of the monsoon in the 30-90 days band. In this paper, we investigate mechanisms of the Sea Surface Temperature (SST) signature of this atmospheric variability, using a combination of observational datasets and Ocean General Circulation Model sensitivity experiments. In addition to the previously-reported intraseasonal SST signature in the Bay of Bengal, observations show clear SST signals in the Arabian Sea related to the active/break cycle of the monsoon. As the atmospheric intraseasonal oscillation moves northward, SST variations appear first at the southern tip of India (day 0), then in the Somali upwelling region (day 10), northern Bay of Bengal (day 19) and finally in the Oman upwelling region (day 23). The Bay of Bengal and Oman signals are most clearly associated with the monsoon active/break index, whereas the relationship with signals near Somali upwelling and the southern tip of India is weaker. In agreement with previous studies, we find that heat flux variations drive most of the intraseasonal SST variability in the Bay of Bengal, both in our model (regression coefficient, 0.9, against ~0.25 for wind stress) and in observations (0.8 regression coefficient); ~60% of the heat flux variation is due do shortwave radiation and ~40% due to latent heat flux. On the other hand, both observations and model results indicate a prominent role of dynamical oceanic processes in the Arabian Sea. Wind-stress variations force about 70-100% of SST intraseasonal variations in the Arabian Sea, through modulation of oceanic processes (entrainment, mixing, Ekman pumping, lateral advection). Our ~100 km resolution model suggests that internal oceanic variability (i.e. eddies) contributes substantially to intraseasonal variability at small-scale in the Somali upwelling region, but does not contribute to large-scale intraseasonal SST variability due to its small spatial scale and random phase relation to the active-break monsoon cycle. The effect of oceanic eddies; however, remains to be explored at a higher spatial resolution.

Fleet Numerical Meteorology and Oceanography Center support for GODAE

NASA Astrophysics Data System (ADS)

Dimitriou, D.; Sharfstein, P.; Ignaszewski, M.; Clancy, M.

2003-04-01

The U.S. Navy's Fleet Numerical Meteorology and Oceanography Center (FNMOC; see http://www.fnmoc.navy.mil/), located in Monterey, CA, is the lead activity within the U.S. Department of Defense (DoD) for numerical weather prediction and coupled air-sea modeling. FNMOC fulfills this role through means of a suite of sophisticated global and regional meteorological and oceanographic (METOC) models, extending from the top of the atmosphere to the bottom of the ocean, which is supported by one of the world's most complete real-time METOC databases. Fleet Numerical operates around-the-clock, 365 days per year and distributes METOC products to military and civilian users around the world, both ashore and afloat, through a variety of means, including a rapidly growing and innovative use of Web technology. FNMOC's customers include all branches of the Department of Defense (DoD), other government organizations such as the National Weather Service, private companies such as the Weather Channel, a number of colleges and universities, and the general public. FNMOC acquires and processes over 6 million METOC observations per day—creating one of the world's most comprehensive real-time databases of meteorological and oceanographic observations for assimilation into its models. FNMOC employs three primary models, the Navy Operational Global Atmospheric Prediction System (NOGAPS), the Coupled Ocean/Atmosphere Mesoscale Prediction System (COAMPS), and the WaveWatch III model (WW3), along with a number of specialized models and related applications. NOGAPS is a global weather model, driving nearly all other FNMOC models and applications in some fashion. COAMPS is a high-resolution regional model that has proved to be particularly valuable for forecasting weather and ocean conditions in highly complex coastal areas. WW3 is a state-of-the-art ocean wave model that is employed both globally and regionally in support of a wide variety of naval operations. Specialized models support and supplement the main models with predictions of ocean thermal structure, ocean currents, and other important data. In general, FNMOC strives to treat the air-ocean environment as a fully integrated system, from the top of the atmosphere to the bottom of the ocean, placing special emphasis on the air-ocean interface. FNMOC also hosts the USGODAE Server (see http://www.usgodae.org). Ongoing development of this system is being done through a partnership of FNMOC and NOAA's Pacific Marine Environmental Lab (PMEL), with oversight from the U.S. Global Ocean Data Assimilation Experiment (GODAE) Steering Committee and funding from the Office of Naval Research (ONR). The USGODAE Server hosts in-situ oceanographic data, atmospheric forcing fields suitable for driving ocean models and unique GODAE data sets, including demonstration ocean model products. The USGODAE Server contains fixed and drifting buoy data, bathythermograph data, PALACE float data, ship data and CMAN data. It also includes TOPEX, GFO, and ERS altimeter data, AVHRR SST retrievals, DMSP sea ice concentration retrievals and meteorological observations. The USGODAE Server also functions as one of two global repositories or Global Data Assembly Centers (GDACs) for data from the Argo global array of temperature/salinity profiling floats. Included in these online data sets are those from Canada (MEDS) with 67 floats and 1900 station files from April 2001 to present, Japan (JMA) with 97 floats and 2700 station files from April 2000 to present, and the U.S. (AOML) with 304 floats and 9800 station files from August 1997 to present, and France (CORIOLIS) with 121 floats and 5396 station files from early 2001 to present. On the USGODAE Server the Argo GDAC Web Interface allows users to easily select data based on time, region, Data Assembly Center (DAC), or float ID. Users can download float profile files, trajectory files, or technical data files. The atmospheric forcing fields hosted on the USGODAE Server are from both FNMOC and the National Centers for Environmental Prediction (NCEP). The FNMOC fields include output from both NOGAPS and COAMPS, with the COAMPS products obtained from the four regional areas surrounding the continental United States. Additionally, the server mirrors the METEO France Satellite Application Facility (SAF) ftp site, which provides surface radiative fluxes, wind vectors, sea-surface temperature fields, and sea ice. To facilitate access and visualization of USGODAE data sets, PMEL has developed the GODAE Live Access Server (LAS) software. LAS enables the Web user to visualize data with on-the-fly graphics, request custom subsets of variables in a choice of file formats, access background reference material about the data (i.e., metadata), and compare (e.g., difference) variables from different data sets. The USGODAE Server also uses the Grid Analysis and Display System (GrADS)/Distributed Oceanographic Data System (DODS) software from the Center for Ocean Land Atmosphere (COLA)/Institute of Global Environment and Society (IGES), serving NOGAPS, COAMPS and NCEP fields as time-aggregated DODS data sets. A thumbnail generator creates preview images for all non-gridded data files on the server, giving users the opportunity to view the contents of large in-situ and satellite data files before downloading them. The USGODAE Server has become a ``one-stop shop" for GODAE researchers and others requiring data to support global ocean modelling studies. As the execution phase for GODAE approaches, additional data sets and data access capabilities will be added to the server. An exciting new aspect of this will be the inclusion of demonstration model products produced by GODAE ocean modelers from around the world. As the server is populated with these products, it is expected to become a significant enabler and focal point for ocean model inter-comparison studies.

Elastic parabolic equation solutions for underwater acoustic problems using seismic sources.

PubMed

Frank, Scott D; Odom, Robert I; Collis, Jon M

2013-03-01

Several problems of current interest involve elastic bottom range-dependent ocean environments with buried or earthquake-type sources, specifically oceanic T-wave propagation studies and interface wave related analyses. Additionally, observed deep shadow-zone arrivals are not predicted by ray theoretic methods, and attempts to model them with fluid-bottom parabolic equation solutions suggest that it may be necessary to account for elastic bottom interactions. In order to study energy conversion between elastic and acoustic waves, current elastic parabolic equation solutions must be modified to allow for seismic starting fields for underwater acoustic propagation environments. Two types of elastic self-starter are presented. An explosive-type source is implemented using a compressional self-starter and the resulting acoustic field is consistent with benchmark solutions. A shear wave self-starter is implemented and shown to generate transmission loss levels consistent with the explosive source. Source fields can be combined to generate starting fields for source types such as explosions, earthquakes, or pile driving. Examples demonstrate the use of source fields for shallow sources or deep ocean-bottom earthquake sources, where down slope conversion, a known T-wave generation mechanism, is modeled. Self-starters are interpreted in the context of the seismic moment tensor.

The influence of meridional ice transport on Europa's ocean stratification and heat content

NASA Astrophysics Data System (ADS)

Zhu, Peiyun; Manucharyan, Georgy E.; Thompson, Andrew F.; Goodman, Jason C.; Vance, Steven D.

2017-06-01

Jupiter's moon Europa likely hosts a saltwater ocean beneath its icy surface. Geothermal heating and rotating convection in the ocean may drive a global overturning circulation that redistributes heat vertically and meridionally, preferentially warming the ice shell at the equator. Here we assess the previously unconstrained influence of ocean-ice coupling on Europa's ocean stratification and heat transport. We demonstrate that a relatively fresh layer can form at the ice-ocean interface due to a meridional ice transport forced by the differential ice shell heating between the equator and the poles. We provide analytical and numerical solutions for the layer's characteristics, highlighting their sensitivity to critical ocean parameters. For a weakly turbulent and highly saline ocean, a strong buoyancy gradient at the base of the freshwater layer can suppress vertical tracer exchange with the deeper ocean. As a result, the freshwater layer permits relatively warm deep ocean temperatures.

The influence of meridional ice transport on Europa's ocean stratification and heat content

NASA Astrophysics Data System (ADS)

Zhu, P.; Manucharyan, G.; Thompson, A. F.; Goodman, J. C.; Vance, S.

2017-12-01

Jupiter's moon Europa likely hosts a saltwater ocean beneath its icy surface. Geothermal heating and rotating convection in the ocean may drive a global overturning circulation that redistributes heat vertically and meridionally, preferentially warming the ice shell at the equator. Here we assess thepreviously unconstrained influence of ocean-ice coupling on Europa's ocean stratification and heat transport. We demonstrate that a relatively fresh layer can form at the ice-ocean interface due to a meridional ice transport forced by the differential ice shell heating between the equator and the poles. We provide analytical and numerical solutions for the layer's characteristics, highlighting their sensitivity to critical ocean parameters. For a weakly turbulent and highly saline ocean, a strong buoyancy gradient at the base of the freshwater layer can suppress vertical tracer exchange with the deeper ocean. As a result, the freshwater layer permits relatively warm deep ocean temperatures.

ASTRAL Model. Volume 2: Software Implementation

DTIC Science & Technology

1979-01-01

Commander Fleet Air, Mediterranean Commander, Antisubmarine War Force U.S. Sixth Fleet Commanding Officer FPO New York 09521 1 Fleet Weather Central...Technology, Inc. I Attn: Dr. S. C. Daubin Route 2 North Stonington, Connecticut 06359 Attn: S. Elam 1 I *--4-- I I Ocean Data Systems, Inc. TRACOR, Inc...APPLICATIONS, INC. 8400 Westpark Drive, McLean, Virginia 22101 Telephone 703/821-4300 S 29082-21227 ’Id _9 0 8i•i•F:• • I U CONTENTS Page 1 1 INTRODUCTION

Interior Pathways to Dissipation of Mesoscale Energy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nadiga, Balasubramanya T.

This talk at Goethe University asks What Powers Overturning Circulation? How does Ocean Circulation Equilibrate? There is a HUGE reservoir of energy sitting in the interior ocean. Can fluid dynamic instabilities contribute to the mixing required to drive global overturning circulation? Study designed to eliminate distinguished horizontal surfaces such as bottom BL and surface layer

The Influence of Midlatitude Ocean-Atmosphere Coupling on the Low-Frequency Variability of a GCM. Part I: No Tropical SST Forcing*.

NASA Astrophysics Data System (ADS)

Bladé, Ileana

1997-08-01

This study examines the extent to which the thermodynamic interactions between the midlatitude atmosphere and the underlying oceanic mixed layer contribute to the low-frequency atmospheric variability. A general circulation model, run under perpetual northern winter conditions, is coupled to a motionless constant-depth mixed layer in midlatitudes, while elsewhere the sea surface temperature (SST) is kept fixed; interannual tropical SST forcing is not included. It is found that coupling does not modify the spatial organization of the variability. The influence of coupling is manifested as a slight reddening of the spectrum of 500-mb geopotential height and a significant enhancement of the lower-tropospheric thermal variance over the oceans at very low frequencies by virtue of the mixed-layer adjustment to surface air temperature variations that occurs on those timescales. This adjustment effectively reduces the thermal damping of the atmosphere associated with surface heat fluxes (or negative oceanic feedback), thus increasing the thermal variance and the persistence of circulation anomalies.In studying the covariability between ocean and atmosphere it is found that the dominant mode of natural atmospheric variability is coupled to the leading mode of SST in each ocean, with the atmosphere leading the ocean by about one month. The cross-correlation function between oceanic and atmospheric anomalies is strongly asymmetric about zero lag. The SST structures are consistent with direct forcing by the anomalous heat fluxes implied by the concurrent surface air temperature and wind fluctuations. Additionally, composites based on large amplitude SST anomaly events contain no evidence of direct driving of atmospheric perturbations by these SST anomalies. Thus, in terms of the spatial organization of the covariability and the evolution of the coupled system from one regime to another, large-scale air-sea interaction in the model is characterized by one-way atmospheric forcing of the mixed layer.These results are qualitatively consistent with those from an earlier idealized study. They imply a subtle but fundamental role for the midlatitude oceans as stabilizing rather than directly generating atmospheric anomalies. It is argued that this scenario is relevant to the dynamics of extratropical atmosphere-ocean coupling on intraseasonal timescales at least: the model is able to qualitatively reproduce the temporal and spatial characteristics of the observed dominant patterns of interaction on these timescales, particularly over the Atlantic.

Quantifying trace element and isotope fluxes at the ocean-sediment boundary: a review.

PubMed

Homoky, William B; Weber, Thomas; Berelson, William M; Conway, Tim M; Henderson, Gideon M; van Hulten, Marco; Jeandel, Catherine; Severmann, Silke; Tagliabue, Alessandro

2016-11-28

Quantifying fluxes of trace elements and their isotopes (TEIs) at the ocean's sediment-water boundary is a pre-eminent challenge to understand their role in the present, past and future ocean. There are multiple processes that drive the uptake and release of TEIs, and properties that determine their rates are unevenly distributed (e.g. sediment composition, redox conditions and (bio)physical dynamics). These factors complicate our efforts to find, measure and extrapolate TEI fluxes across ocean basins. GEOTRACES observations are unveiling the oceanic distributions of many TEIs for the first time. These data evidence the influence of the sediment-water boundary on many TEI cycles, and underline the fact that our knowledge of the source-sink fluxes that sustain oceanic distributions is largely missing. Present flux measurements provide low spatial coverage and only part of the empirical basis needed to predict TEI flux variations. Many of the advances and present challenges facing TEI flux measurements are linked to process studies that collect sediment cores, pore waters, sinking material or seawater in close contact with sediments. However, such sampling has not routinely been viable on GEOTRACES expeditions. In this article, we recommend approaches to address these issues: firstly, with an interrogation of emergent data using isotopic mass-balance and inverse modelling techniques; and secondly, by innovating pursuits of direct TEI flux measurements. We exemplify the value of GEOTRACES data with a new inverse model estimate of benthic Al flux in the North Atlantic Ocean. Furthermore, we review viable flux measurement techniques tailored to the sediment-water boundary. We propose that such activities are aimed at regions that intersect the GEOTRACES Science Plan on the basis of seven criteria that may influence TEI fluxes: sediment provenance, composition, organic carbon supply, redox conditions, sedimentation rate, bathymetry and the benthic nepheloid inventory.This article is part of the themed issue 'Biological and climatic impacts of ocean trace element chemistry'. © 2015 The Authors.

Quantifying trace element and isotope fluxes at the ocean-sediment boundary: a review

NASA Astrophysics Data System (ADS)

Homoky, William B.; Weber, Thomas; Berelson, William M.; Conway, Tim M.; Henderson, Gideon M.; van Hulten, Marco; Jeandel, Catherine; Severmann, Silke; Tagliabue, Alessandro

2016-11-01

Quantifying fluxes of trace elements and their isotopes (TEIs) at the ocean's sediment-water boundary is a pre-eminent challenge to understand their role in the present, past and future ocean. There are multiple processes that drive the uptake and release of TEIs, and properties that determine their rates are unevenly distributed (e.g. sediment composition, redox conditions and (bio)physical dynamics). These factors complicate our efforts to find, measure and extrapolate TEI fluxes across ocean basins. GEOTRACES observations are unveiling the oceanic distributions of many TEIs for the first time. These data evidence the influence of the sediment-water boundary on many TEI cycles, and underline the fact that our knowledge of the source-sink fluxes that sustain oceanic distributions is largely missing. Present flux measurements provide low spatial coverage and only part of the empirical basis needed to predict TEI flux variations. Many of the advances and present challenges facing TEI flux measurements are linked to process studies that collect sediment cores, pore waters, sinking material or seawater in close contact with sediments. However, such sampling has not routinely been viable on GEOTRACES expeditions. In this article, we recommend approaches to address these issues: firstly, with an interrogation of emergent data using isotopic mass-balance and inverse modelling techniques; and secondly, by innovating pursuits of direct TEI flux measurements. We exemplify the value of GEOTRACES data with a new inverse model estimate of benthic Al flux in the North Atlantic Ocean. Furthermore, we review viable flux measurement techniques tailored to the sediment-water boundary. We propose that such activities are aimed at regions that intersect the GEOTRACES Science Plan on the basis of seven criteria that may influence TEI fluxes: sediment provenance, composition, organic carbon supply, redox conditions, sedimentation rate, bathymetry and the benthic nepheloid inventory. This article is part of the themed issue 'Biological and climatic impacts of ocean trace element chemistry'.

Coherent climate anomalies over the Indo-western Pacific in post-El Niño summer

NASA Astrophysics Data System (ADS)

Kosaka, Y.; Xie, S. P.; DU, Y.; Hu, K.; Chowdary, J. S.; Huang, G.

2016-12-01

El Niño typically peaks in boreal winter, and the associated equatorial Pacific sea surface temperature (SST) signal dissipates before subsequent summer. Its impact, however, outlasts until boreal summer in the Indo-western Pacific, featuring basin-wide Indian Ocean warming and tropical Northwestern Pacific cooling accompanied by the Pacific-Japan (PJ) teleconnection pattern with surface anomalous anticyclone (AAC) extending from the Philippine Sea to the northern Indian Ocean. Two formation mechanisms have been proposed for these climate anomalies in post-El Niño-Southern Oscillation (ENSO) summer. One hypothesis invokes the wind-evaporation-SST (WES) feedback in the tropical Northwestern Pacific, while the other points to inter-basin feedback between the Indian Ocean and tropical Northwestern Pacific. Based on a coupled model experiment, we propose an ocean-atmosphere coupled mode that synthesizes the two mechanisms. This Indo-western Pacific Ocean capacitor (IPOC) mode evolves seasonally from spring to summer under seasonal migration of background state. In spring, the WES feedback is operative in association with the tropical Northwestern Pacific cooling, while in summer the Indian Ocean warming and the inter-basin interaction maintains the AAC. While the IPOC mode is independent of ENSO in mechanism, ENSO can drive this mode in its decay phase. This excitation, however, has undergone substantial interdecadal modulations, depending on ENSO amplitude and persistence of Indian Ocean warming. The ENSO-IPOC correlation is high after the mid-1970s and at the beginning of the 20th century, but low in between.

Water-mass formation and Sverdrup dynamics; a comparison between climatology and a coupled ocean-atmosphere model

NASA Astrophysics Data System (ADS)

England, Matthew H.; Tomczak, Matthias; Stuart Godfrey, J.

1992-06-01

The coupled ocean-atmosphere model integrations of Manabe and Stouffer (1988) are compared with climatological distributions of depth-integrated flow and water-mass formation. The description of the ocean circulation in their two quasi-stable equilibria is extended to include an analysis of the horizontal and meridional transport as well as the water-mass formation and vertical motion in the model. In particular, the wind-driven Sverdrup flow is computed and compared with the actual mass transport streamfunction of the model. It is found that a Sverdrup model of depth-integrated flow captures the major features of the coupled model's ocean circulation, except near region of deep water formation, where the thermohaline field drives ocean currents and wind-driven flow becomes secondary. The coupled model fails to allow for a barotropic mass transport through the Indonesian Passage. Instead, only baroclinically driven fluxes of heat and freshwater are resolved through the Indonesian Archipelago. The Sverdrup model suggests that a barotropic throughflow would transport about 16 Sv from the Pacific to Indian Oceans. According to Sverdrup dynamics, this would serve to weaken the East Australian Current by about 16 Sv and strengthen the Agulhas Current by the same amount. Recent integrations of a World Ocean model with and without a barotropic throughflow in the Indonesian Passage suggest that the modelled heat transport is sensitive to the nature of flow through the Indonesian Archipelago. From' a comparison of observed and simulated water mass properties, it is shown that some major aspects of the global-scale water masses are not captured by the coupled model. This reveals a shortcoming of the model's ability to represent the global-scale heat and freshwater balances. For example, there is an unrealistically intense halocline in the immediate vicinity of Antartica, prohibiting the formation of bottom water in the Weddell and Ross Seas. Also, no low salinity traces of Antarctic or North Pacific Intermediate Water appear in the model integrations, primarily because there is no source of sufficiently dense bottom water adjacent to Antarctica. Without this dense bottom water, the "would-be" intermediate water at 60°S sinks to great depths and actually becomes the model ocean's bottom water. Then, the simulated bottom water is too fresh and warm in the climate model, matching the temperature—salinity signature of Antarctic Intermediate Water. In the North Atlantic, whilst deep water formation appears in one of the climate states of Manabe and Stouffer (1988), its downward penetration is not as deep as observed. This is because their deep North Atlantic is not ventilated by the thermohaline overturning of warm salty North Atlantic Deep Water. Instead, a deep overturning cell centred near the equator transports relatively fresh water into the region. In contrast, the location and strength of Central Water formation agrees well with climatology.

Sensitivity of the Southern Ocean overturning circulation to surface buoyancy forcing

NASA Astrophysics Data System (ADS)

Morrison, A.; Hogg, A.; Ward, M.

2011-12-01

The southern limb of the ocean's meridional overturning circulation plays a key role in the Earth's response to climate change. The rise in atmospheric CO2 during glacial-interglacial transitions has been attributed to outgassing of enhanced upwelling water masses in the Southern Ocean. However a dynamical understanding of the physical mechanisms driving the change in overturning is lacking. Previous modelling studies of the Southern Ocean have focused on the effect of wind stress forcing on the overturning, while largely neglecting the response of the upper overturning cell to changes in surface buoyancy forcing. Using a series of eddy-permitting, idealised simulations of the Southern Ocean, we show that surface buoyancy forcing in the mid-latitudes is likely to play a significant role in setting the strength of the overturning circulation. Air-sea fluxes of heat and precipitation over the Antarctic Circumpolar Current region act to convert dense upwelled water masses into lighter waters at the surface. Additional fluxes of heat or freshwater thereby facilitate the meridional overturning up to a theoretical limit derived from Ekman transport. The sensitivity of the overturning to surface buoyancy forcing is strongly dependent on the relative locations of the wind stress profile, buoyancy forcing and upwelling region. The idealised model results provide support for the hypothesis that changes in upwelling during deglaciations may have been driven by changes in heat and freshwater fluxes, instead of, or in addition to, changes in wind stress. Morrison, A. K., A. M. Hogg, and M. L. Ward (2011), Sensitivity of the Southern Ocean overturning circulation to surface buoyancy forcing, Geophys. Res. Lett., 38, L14602, doi:10.1029/2011GL048031.

Turtle groups or turtle soup: dispersal patterns of hawksbill turtles in the Caribbean.

PubMed

Blumenthal, J M; Abreu-Grobois, F A; Austin, T J; Broderick, A C; Bruford, M W; Coyne, M S; Ebanks-Petrie, G; Formia, A; Meylan, P A; Meylan, A B; Godley, B J

2009-12-01

Despite intense interest in conservation of marine turtles, spatial ecology during the oceanic juvenile phase remains relatively unknown. Here, we used mixed stock analysis and examination of oceanic drift to elucidate movements of hawksbill turtles (Eretmochelys imbricata) and address management implications within the Caribbean. Among samples collected from 92 neritic juvenile hawksbills in the Cayman Islands we detected 11 mtDNA control region haplotypes. To estimate contributions to the aggregation, we performed 'many-to-many' mixed stock analysis, incorporating published hawksbill genetic and population data. The Cayman Islands aggregation represents a diverse mixed stock: potentially contributing source rookeries spanned the Caribbean basin, delineating a scale of recruitment of 200-2500 km. As hawksbills undergo an extended phase of oceanic dispersal, ocean currents may drive patterns of genetic diversity observed on foraging aggregations. Therefore, using high-resolution Aviso ocean current data, we modelled movement of particles representing passively drifting oceanic juvenile hawksbills. Putative distribution patterns varied markedly by origin: particles from many rookeries were broadly distributed across the region, while others would appear to become entrained in local gyres. Overall, we detected a significant correlation between genetic profiles of foraging aggregations and patterns of particle distribution produced by a hatchling drift model (Mantel test, r = 0.77, P < 0.001; linear regression, r = 0.83, P < 0.001). Our results indicate that although there is a high degree of mixing across the Caribbean (a 'turtle soup'), current patterns play a substantial role in determining genetic structure of foraging aggregations (forming turtle groups). Thus, for marine turtles and other widely distributed marine species, integration of genetic and oceanographic data may enhance understanding of population connectivity and management requirements.

Influence of 1997/98 and 2006/2007 Indian Ocean Dipole on Phytoplankton Composition in the Eastern Tropical Indian Ocean

NASA Astrophysics Data System (ADS)

Mahapatra, K.; Okada, Y.

2016-02-01

The influence of Indian Ocean Dipole (IOD) events of varied intensity co-occurred with El Niño/Southern Oscillation (ENSO) in 1997/98 and 2006/2007 on phytoplankton functional types (PFTs) was assessed in the eastern tropical Indian Ocean using the NASA Ocean Biogeochemical Model (NOBM) and particle size distribution (PSD) parameters retrieved from satellite derived ocean color data. Response of the PFTs to the IOD events of 1997/98 and 2006/2007 was varied in term of magnitude and duration. Nitrate, chlorophyll and 2 PFTs (diatoms and chlorophytes) out of 4 PFTs (Diatoms, Chlorophytes, Coccolithophores and Cyanobacteria) were strongly correlated with the Dipole Mode Indices. The NOBM provided insight to the course of events leading to perturbations and evolution of biogeochemical processes associated with the IOD in a multi-phytoplankton context, against the backdrop of circulation and turbulence dynamics, irradiance availability, and the interaction among different PFTs. Different phases of the IOD cycle were well captured in the evolution of phytoplankton dynamics. Satellite-based retrievals of PSD parameters further characterized the specific biogeochemical setup that facilitated the PFTs to thrive and cross-dominate each other. We examined the potential impact of the IOD/ENSO events on the PFT-specific primary production. Significant correlation was noticed between DMI and PFT-specific primary production of diatoms and chlorophytes. We highlighted the need (1) to develop regional biogeochemical models to overcome the gaps in our understanding and elucidate the precise mechanism that drive the biogeochemical fluctuations in the region (2) to pursue further research on phenological aspects of PFTs to understand potential impact of climatological change on phytoplankton community and on annually recurring cycle of pelagic trophodynamics and ecosystem functions.

Historical processes and contemporary ocean currents drive genetic structure in the seagrass Thalassia hemprichii in the Indo-Australian Archipelago.

PubMed

Hernawan, Udhi E; van Dijk, Kor-Jent; Kendrick, Gary A; Feng, Ming; Biffin, Edward; Lavery, Paul S; McMahon, Kathryn

2017-02-01

Understanding spatial patterns of gene flow and genetic structure is essential for the conservation of marine ecosystems. Contemporary ocean currents and historical isolation due to Pleistocene sea level fluctuations have been predicted to influence the genetic structure in marine populations. In the Indo-Australian Archipelago (IAA), the world's hotspot of marine biodiversity, seagrasses are a vital component but population genetic information is very limited. Here, we reconstructed the phylogeography of the seagrass Thalassia hemprichii in the IAA based on single nucleotide polymorphisms (SNPs) and then characterized the genetic structure based on a panel of 16 microsatellite markers. We further examined the relative importance of historical isolation and contemporary ocean currents in driving the patterns of genetic structure. Results from SNPs revealed three population groups: eastern Indonesia, western Indonesia (Sunda Shelf) and Indian Ocean; while the microsatellites supported five population groups (eastern Indonesia, Sunda Shelf, Lesser Sunda, Western Australia and Indian Ocean). Both SNPs and microsatellites showed asymmetrical gene flow among population groups with a trend of southwestward migration from eastern Indonesia. Genetic diversity was generally higher in eastern Indonesia and decreased southwestward. The pattern of genetic structure and connectivity is attributed partly to the Pleistocene sea level fluctuations modified to a smaller level by contemporary ocean currents. © 2016 John Wiley & Sons Ltd.

Dynamical ocean-atmospheric drivers of floods and droughts

NASA Astrophysics Data System (ADS)

Perdigão, Rui A. P.; Hall, Julia

2014-05-01

The present study contributes to a better depiction and understanding of the "facial expression" of the Earth in terms of dynamical ocean-atmospheric processes associated to both floods and droughts. For this purpose, the study focuses on nonlinear dynamical and statistical analysis of ocean-atmospheric mechanisms contributing to hydrological extremes, broadening the analytical hydro-meteorological perspective of floods and hydrological droughts to driving mechanisms and feedbacks at the global scale. In doing so, the analysis of the climate-related causality of hydrological extremes is not limited to the synoptic situation in the region where the events take place. Rather, it goes further in the train of causality, peering into dynamical interactions between planetary-scale ocean and atmospheric processes that drive weather regimes and influence the antecedent and event conditions associated to hydrological extremes. In order to illustrate the approach, dynamical ocean-atmospheric drivers are investigated for a selection of floods and droughts. Despite occurring in different regions with different timings, common underlying mechanisms are identified for both kinds of hydrological extremes. For instance, several analysed events are seen to have resulted from a large-scale atmospheric situation consisting on standing planetary waves encircling the northern hemisphere. These correspond to wider vortices locked in phase, resulting in wider and more persistent synoptic weather patterns, i.e. with larger spatial and temporal coherence. A standing train of anticyclones and depressions thus encircled the mid and upper latitudes of the northern hemisphere. The stationary regime of planetary waves occurs when the mean eastward zonal flow decreases up to a point in which it no longer exceeds the westward phase propagation of the Rossby waves produced by the latitude-varying Coriolis effect. The ocean-atmospheric causes for this behaviour and consequences on hydrological extremes are investigated and the findings supported with spatiotemporal geostatistical analysis and nonlinear geophysical models. Overall, the study provides a three-fold contribution to the research on hydrological extremes: Firstly, it improves their physical attribution by better understanding the dynamical reasons behind the meteorological drivers. Secondly, it brings out fundamental early warning signs for potential hydrological extremes, by bringing out global ocean-atmospheric features that manifest themselves much earlier than the regional weather patterns. Thirdly, it provides tools for addressing and understanding hydrological regime changes at wider spatiotemporal scales, by providing links to planetary-scale dynamical processes that play a crucial role in multi-decadal global climate variability.

Effect of Sulfate Aerosol Geoengineering on Tropical cyclones

NASA Astrophysics Data System (ADS)

Wang, Q.; Moore, J.; Ji, D.

2017-12-01

Variation in tropical cyclone (TC) number and intensity is driven in part by changes in the thermodynamics that can be defined by ocean and atmospheric variables. Genesis Potential Index (GPI) and ventilation index (VI) are combinations of potential intensity, vertical wind shear, relative humidity, midlevel entropy deficit, and absolute vorticity that quantify thermodynamic forcing of TC activity under changed climates, and can be calculated from climate model output. Here we use five CMIP5 models running the RCP45 experiment the Geoengineering Model Intercomparison Project (GeoMIP) stratospheric aerosol injection G4 experiment to calculate the two indices over the 2020 to 2069 period. Globally, GPI under G4 is lower than under RCP45, though both have a slight increasing trend. Spatial patterns in the relative effectiveness of geoengineering show reductions in TC in all models in the North Atlantic basin, and northern Indian Ocean in all except NorESM1-M. In the North Pacific, most models also show relative reductions under G4. VI generally coincide with the GPI patterns. Most models project Potential intensity and Relative Humidity to be the dominant variable to affect genesis potential. Changes in vertical wind shear and vorticity are small with scatter across different models and ocean basins. We find that tropopause temperature maybe as important as sea surface temperature in effecting TC genesis. Thus stratospheric aerosol geoengineering impacts on potential intensity and hence TC intensity are reasonably consistent, but probably underestimated by statistical forecasts of Tropical North Atlantic hurricane activity driven by sea surface temperatures alone. However the impacts of geoengineering on other ocean basins are more difficult to assess, and require more complete understanding of their driving parameters under present day climates. Furthermore, the possible effects of stratospheric injection on chemical reactions in the stratosphere, such as ozone, are not well rendered in the models used so far.

Vital Signs: Seismology of Icy Ocean Worlds

NASA Astrophysics Data System (ADS)

Vance, Steven D.; Kedar, Sharon; Panning, Mark P.; Stähler, Simon C.; Bills, Bruce G.; Lorenz, Ralph D.; Huang, Hsin-Hua; Pike, W. T.; Castillo, Julie C.; Lognonné, Philippe; Tsai, Victor C.; Rhoden, Alyssa R.

2018-01-01

Ice-covered ocean worlds possess diverse energy sources and associated mechanisms that are capable of driving significant seismic activity, but to date no measurements of their seismic activity have been obtained. Such investigations could reveal the transport properties and radial structures, with possibilities for locating and characterizing trapped liquids that may host life and yielding critical constraints on redox fluxes and thus on habitability. Modeling efforts have examined seismic sources from tectonic fracturing and impacts. Here, we describe other possible seismic sources, their associations with science questions constraining habitability, and the feasibility of implementing such investigations. We argue, by analogy with the Moon, that detectable seismic activity should occur frequently on tidally flexed ocean worlds. Their ices fracture more easily than rocks and dissipate more tidal energy than the <1 GW of the Moon and Mars. Icy ocean worlds also should create less thermal noise due to their greater distance and consequently smaller diurnal temperature variations. They also lack substantial atmospheres (except in the case of Titan) that would create additional noise. Thus, seismic experiments could be less complex and less susceptible to noise than prior or planned planetary seismology investigations of the Moon or Mars.

Meridional contrasts in productivity changes driven by the Cenozoic opening of Drake Passage

NASA Astrophysics Data System (ADS)

Donnadieu, Y.; Ladant, J. B.; Bopp, L.; Wilson, P. A.; Lear, C. H.

2017-12-01

The progressive opening of Drake Passage across the Eocene and the Oligocene occurs contemporaneously to the long-term global cooling of the late Eocene, which culminated with the Eocene-Oligocene glaciation of Antarctica. Atmospheric pCO2 decline during the late Eocene is thought to have played a major role in the climatic shifts of the Eocene-Oligocene boundary, yet reasons behind CO2 variations remain obscure. Changes in marine productivity affecting the biological oceanic carbon pump represent a possible cause. Here, we explore whether and how the opening of Drake Passage may have affected the marine biogeochemistry, and in particular paleoproductivity changes, with the use of a fully coupled atmosphere-ocean-biogeochemical model (IPSL-CM5A). We find that the simulated changes to Drake Passage opening exhibit a uniform decrease in the low latitudes while the high latitude response is more spatially heterogeneous. Mechanistically, the low latitude productivity decrease is a consequence of the dramatic reorganization of the ocean circulation when Drake Passage opens, as the shift from a well ventilated to a swampier ocean drives nutrient depletion in the low latitudes. In the high latitudes, the onset of the Antarctic Circumpolar Current in the model exerts a strong control both on nutrient availability but also on regions of deep water formation, which results in non-uniform patterns of productivity change in the Southern Ocean. The qualitative agreement between geographically diverse long-term paleoproductivity records and the simulated variations suggests that the opening of Drake Passage may contribute to part of the long-term paleoproductivity signal recorded in the data.

Southern Ocean Deep-Convection as a Driver of Centennial-to-Millennial-Scale Climate Variability at Southern High Latitudes

NASA Astrophysics Data System (ADS)

Pedro, J. B.; Martin, T.; Steig, E. J.; Jochum, M.; Park, W.; Rasmussen, S.

2015-12-01

Antarctic Isotope Maxima (AIM) are centennial-to-millennial scale warming events observed in Antarctic ice core records from the last glacial period and deglaciation. Mounting evidence links AIM events to parallel variations in atmospheric CO2, Southern Ocean (SO) sea surface temperatures and Antarctic Bottom Water production. According to the prevailing view, AIM events are forced from the North Atlantic by melt-water discharge from ice sheets suppressing the production of North Atlantic Deep Water and associated northward heat transport in the Atlantic. However observations and model studies increasingly suggest that melt-water fluxes have the wrong timing to be invoked as such a trigger. Here, drawing on results form the Kiel Climate Model, we present an alternative hypothesis in which AIM events are forced via internal oscillations in SO deep-convection. The quasi-periodic timescale of deep-convection events is set by heat (buoyancy) accumulation at SO intermediate depths and stochastic variability in sea ice conditions and freshening at the surface. Massive heat release from the SO convective zone drives Antarctic and large-scale southern hemisphere warming via a two-stage process involving changes in the location of Southern Ocean fronts, in the strength and intensity of the Westerlies and in meridional ocean and atmospheric heat flux anomalies. The potential for AIM events to be driven by internal Southern Ocean processes and the identification of time-lags internal to the southern high latitudes challenges conventional views on the North Atlantic as the pacemaker of millennial-scale climate variability.

Indian Ocean Dipolelike Variability in the CSIRO Mark 3 Coupled Climate Model.

NASA Astrophysics Data System (ADS)

Cai, Wenju; Hendon, Harry H.; Meyers, Gary

2005-05-01

Coupled ocean-atmosphere variability in the tropical Indian Ocean is explored with a multicentury integration of the Commonwealth Scientific and Industrial Research Organisation (CSIRO) Mark 3 climate model, which runs without flux adjustment. Despite the presence of some common deficiencies in this type of coupled model, zonal dipolelike variability is produced. During July through November, the dominant mode of variability of sea surface temperature resembles the observed zonal dipole and has out-of-phase rainfall variations across the Indian Ocean basin, which are as large as those associated with the model El Niño-Southern Oscillation (ENSO). In the positive dipole phase, cold SST anomaly and suppressed rainfall south of the equator on the Sumatra-Java coast drives an anticyclonic circulation anomaly that is consistent with the steady response (Gill model) to a heat sink displaced south of the equator. The northwest-southeast tilting Sumatra-Java coast results in cold sea surface temperature (SST) centered south of the equator, which forces anticylonic winds that are southeasterly along the coast, which thus produces local upwelling, cool SSTs, and promotes more anticylonic winds; on the equator, the easterlies raise the thermocline to the east via upwelling Kelvin waves and deepen the off-equatorial thermocline to the west via off-equatorial downwelling Rossby waves. The model dipole mode exhibits little contemporaneous relationship with the model ENSO; however, this does not imply that it is independent of ENSO. The model dipole often (but not always) develops in the year following El Niño. It is triggered by an unrealistic transmission of the model's ENSO discharge phase through the Indonesian passages. In the model, the ENSO discharge Rossby waves arrive at the Sumatra-Java coast some 6 to 9 months after an El Niño peaks, causing the majority of model dipole events to peak in the year after an ENSO warm event. In the observed ENSO discharge, Rossby waves arrive at the Australian northwest coast. Thus the model Indian Ocean dipolelike variability is triggered by an unrealistic mechanism. The result highlights the importance of properly representing the transmission of Pacific Rossby waves and Indonesian throughflow in the complex topography of the Indonesian region in coupled climate models.

Rising sea levels will reduce extreme temperature variations in tide-dominated reef habitats

PubMed Central

Lowe, Ryan Joseph; Pivan, Xavier; Falter, James; Symonds, Graham; Gruber, Renee

2016-01-01

Temperatures within shallow reefs often differ substantially from those in the surrounding ocean; therefore, predicting future patterns of thermal stresses and bleaching at the scale of reefs depends on accurately predicting reef heat budgets. We present a new framework for quantifying how tidal and solar heating cycles interact with reef morphology to control diurnal temperature extremes within shallow, tidally forced reefs. Using data from northwestern Australia, we construct a heat budget model to investigate how frequency differences between the dominant lunar semidiurnal tide and diurnal solar cycle drive ~15-day modulations in diurnal temperature extremes. The model is extended to show how reefs with tidal amplitudes comparable to their depth, relative to mean sea level, tend to experience the largest temperature extremes globally. As a consequence, we reveal how even a modest sea level rise can substantially reduce temperature extremes within tide-dominated reefs, thereby partially offsetting the local effects of future ocean warming. PMID:27540589

What Drives the Variability of the Atlantic Water Circulation in the Arctic Ocean?

NASA Astrophysics Data System (ADS)

Lique, C.; Johnson, H. L.

2016-02-01

The Atlantic Water (AW) layer in the Arctic Basin is isolated from the atmosphere by the overlaying surface layer; yet observations of the AW pan-Arctic boundary current have revealed that the velocities in this layer exhibit significant variations on all timescales. Here, analysis of a global ocean/sea ice model hindcast, complemented by experiments performed with an idealized process model, are used to investigate what controls the variability of AW circulation, with a focus on the role of wind forcing. The AW circulation carries the imprint of wind variations, both remotely over the Nordic and Barents seas where they force variability on the AW inflow to the Arctic Basin, and locally over the Arctic Basin through the forcing of the wind-driven Beaufort gyre, which modulates and transfers the wind variability to the AW layer. Our results further suggest that understanding variability in the large amount of heat contained within the AW layer requires a better understanding of the circulation within both AW and surface layers.

Development of underwater cutting system by abrasive water-jet

NASA Astrophysics Data System (ADS)

Demura, Kenji; Yamaguchi, Hitoshi

1993-09-01

The technology to cut objects in the ocean's depths with abrasive water jets was examined for possible application in view of the greater water depths and sophistication involved in work on the ocean floor today. A test model was developed to study this technology's safety and practicability. The test model was designed for use at great water depths and has functions and a configuration that are unlike equipment used on land. A continuous, stable supply of abrasive is a distinctive design feature. In land applications, there had been problems with plugged tubes and an uneven supply. For this reason, the abrasive was converted to slurry form, and a continuous pressurized tube pump system was adopted for supply to the nozzle head. Also, a hydraulic motor that does not employ oil or electric power was used to provide an underwater drive that is environment-friendly. The report outlines the technology's general design concept including its distinctive functions and its configuration for use at great depths, and the report provides great detail on the equipment.

Factors controlling the Indian summer monsoon onset in a coupled model

NASA Astrophysics Data System (ADS)

Prodhomme, Chloé; Terray, Pascal; Masson, Sébastien; Izumo, Takeshi

2013-04-01

The observed Indian Summer Monsoon (ISM) onset occurs around 30 May and 2 June, with a standard deviation of 8 to 9 days, according to the estimates. The relationship between interannual variability of the ISM onset and SSTs (Sea Surface Temperature) remains controversial. The role of Indian Ocean SSTs remain unclear, some studies have shown a driving role while other suggests a passive relation between Indian Ocean SSTs and ISM. The intrinsic impact of ENSO (El Nino-Southern Oscillation) is also difficult to estimate from observations alone. Finally, the predictability of the ISM onset remains drastically limited by the inability of both forced and coupled model to reproduce a realistic onset date. In order to measure objectively the ISM onset, different methods have been developed based on rainfall or dynamical indices (Ananthakrishnan and Soman, 1988 ; Wang and Ho 2002 ; Joseph et al. 2006). In the study we use the Tropospheric Temperature Gradient (TTG), which is the difference between the tropospheric temperature in a northern and a southern box in the Indian areas (Xavier et al. 2007). This index measures the dynamical strength of the monsoon and provides a stable and precise onset date consistent with rainfall estimates. In the SINTEX-F2 coupled model, the ISM onset measured with the TTG is delayed of approximately 10 days and is in advance of 6 days in the atmosphere-only (ECHAM) model. The 16 days lag between atmospheric-only and coupled runs suggests a crucial role of the coupling, especially SST biases on the delayed onset. With the help of several sensitivity experiments, this study tries to identify the keys regions influencing the ISM onset. Many studies have shown a strong impact of the Arabian Sea and Indian Ocean SST on the ISM onset. Nevertheless, the correction of the SSTs, based on AVHRR, in the tropical Indian Ocean only slightly corrects the delayed onset in the coupled model, which suggests an impact of SST in others regions on the ISM onset. During May and June, the main tropical SST biases in the coupled model are a strong warm bias in the Atlantic Ocean and a warm bias in the tropical Pacific Ocean, except along the equator around 140°W-100°W, where there is a cold tongue bias. The correction of the warm bias in the Atlantic Ocean slightly improves the onset date. Conversely, the correction of SST biases in the tropical and equatorial Pacific Oceans advances the onset date of 12 and 10 days, respectively, compared to the control coupled run. This result suggests that, at least in this model, the ISM onset is mainly control by the Pacific Ocean SSTs. Even if ENSO has an impact on the onset date it does not explain the delay, which is related to the biased SST mean state in the Pacific Ocean.

Potential impact of remote sensing data on sea-state analysis and prediction

NASA Technical Reports Server (NTRS)

Cardone, V. J.

1983-01-01

The severe North Atlantic storm which damaged the ocean liner Queen Elizabeth 2 (QE2) was studied to assess the impact of remotely sensed marine surface wind data obtained by SEASAT-A, on sea state specifications and forecasts. Alternate representations of the surface wind field in the QE2 storm were produced from the SEASAT enhanced data base, and from operational analyses based upon conventional data. The wind fields were used to drive a high resolution spectral ocean surface wave prediction model. Results show that sea state analyses would have been vastly improved during the period of storm formation and explosive development had remote sensing wind data been available in real time. A modest improvement in operational 12 to 24 hour wave forecasts would have followed automatically from the improved initial state specification made possible by the remote sensing data in both numerical and sea state prediction models. Significantly improved 24 to 48 hour wave forecasts require in addition to remote sensing data, refinement in the numerical and physical aspects of weather prediction models.

Ocean Wave Simulation Based on Wind Field

PubMed Central

2016-01-01

Ocean wave simulation has a wide range of applications in movies, video games and training systems. Wind force is the main energy resource for generating ocean waves, which are the result of the interaction between wind and the ocean surface. While numerous methods to handle simulating oceans and other fluid phenomena have undergone rapid development during the past years in the field of computer graphic, few of them consider to construct ocean surface height field from the perspective of wind force driving ocean waves. We introduce wind force to the construction of the ocean surface height field through applying wind field data and wind-driven wave particles. Continual and realistic ocean waves result from the overlap of wind-driven wave particles, and a strategy was proposed to control these discrete wave particles and simulate an endless ocean surface. The results showed that the new method is capable of obtaining a realistic ocean scene under the influence of wind fields at real time rates. PMID:26808718

Ocean Wave Simulation Based on Wind Field.

PubMed

Li, Zhongyi; Wang, Hao

2016-01-01

Ocean wave simulation has a wide range of applications in movies, video games and training systems. Wind force is the main energy resource for generating ocean waves, which are the result of the interaction between wind and the ocean surface. While numerous methods to handle simulating oceans and other fluid phenomena have undergone rapid development during the past years in the field of computer graphic, few of them consider to construct ocean surface height field from the perspective of wind force driving ocean waves. We introduce wind force to the construction of the ocean surface height field through applying wind field data and wind-driven wave particles. Continual and realistic ocean waves result from the overlap of wind-driven wave particles, and a strategy was proposed to control these discrete wave particles and simulate an endless ocean surface. The results showed that the new method is capable of obtaining a realistic ocean scene under the influence of wind fields at real time rates.

The use of EuroCordex in marine climate projections

NASA Astrophysics Data System (ADS)

Tinker, Jonathan; Palmer, Matthew; Lowe, Jason; Howard, Tom

2017-04-01

The Northwest European Shelf seas (NWS, including the North Sea, Irish Sea and Celtic Sea) are of economic, environmental and cultural importance to a number of European countries. However, their representation by global climate models (GCMs) is very crude, due to their inability to represent the complex geometry and the absence of tides. Therefore, there is a need to employ dynamical downscaling methods when considering the potential impacts of climate change on the European (and other) shelf seas. Using a shelf seas model to dynamically downscale of the ocean component of the GCM is a well established method. While taking open ocean lateral boundary conditions from the GCM ocean is acceptable, using surface flux forcings from the GCM atmosphere is often problematic. The CORDEX project provides an important dataset of high spatial and temporal resolution atmospheric forcings, derived from 'parent' CMIP5 GCM simulations. We drive the NEMO shelf seas model with data from CMIP5 models and EURO-CORDEX Regional Climate Model (RCM) data to produce a set of NWS climate projections. We require relatively high temporal resolution output, and run-off (for the river forcings), and so are limited to a subset of the available EURO-CORDEX RCMs. From these we select two CMIP5 GCMs with the same RCM with two emissions scenarios to give a minimum estimate of GCM model structural and emission scenario uncertainty. Other experiments allow an initial estimate of the uncertainty associated with the model structure of both the shelf seas and the RCM. Our analysis is focused on the uncertainty associated with the mean change in a number of physical marine impacts and the drivers of coastal variability and change, including sea level and the propagation of open ocean signals onto the shelf. Our work is part of the UK Climate Projections (UKCP18) and will inform the following UK Climate Change Risk Assessments, required as part of the Climate Change Act.

Microbial use of gas phase organic compounds in the surface ocean

NASA Astrophysics Data System (ADS)

Arrieta, Jesus M.; Duarte, Carlos M.; Monserrat Sala, M.; Dachs, Jordi

2016-04-01

Large diffusive air-sea fluxes of gas-phase organic carbon (GOC) have been identified, indicating that the ocean may be a major sink for these compounds. However, little is known about the fate of these GOC compounds entering the surface ocean. We report efficient use of atmospheric GOC by marine prokaryotes at different locations in the NE Subtropical Atlantic Ocean, the Arctic Ocean and the Mediterranean Sea. Our results indicate that between 2 to 27% of the prokaryotic carbon demand was supported by GOC. Between 1 and 94% of the GOC entering the ocean was consumed by prokaryotes depending on locations, thus sustaining a disequilibrium, which drives the transfer of GOC from the atmosphere into the ocean. The magnitude of this, previously unnoticed, microbial GOC utilization stresses the need for incorporating the oceanic uptake of gaseous organic carbon into the global carbon budget.

Coupled climate impacts of the Drake Passage and the Panama Seaway

NASA Astrophysics Data System (ADS)

Yang, Simon; Galbraith, Eric; Palter, Jaime

2014-07-01

Tectonically-active gateways between ocean basins have modified ocean circulation over Earth history. Today, the Atlantic and Pacific are directly connected via the Drake Passage, which forms a barrier to the time-mean geostrophic transport between the subtropics and Antarctica. In contrast, during the warm early Cenozoic era, when Antarctica was ice-free, the Drake Passage was closed. Instead, at that time, the separation of North and South America provided a tropical seaway between the Atlantic and Pacific that remained open until the Isthmus of Panama formed in the relatively recent geological past. Ocean circulation models have previously been used to explore the individual impacts of the Drake Passage and the Panama Seaway, but rarely have the two gateways been considered together, and most explorations have used very simple atmospheric models. Here we use a coupled ocean-ice-atmosphere model (GFDL's CM2Mc), to simulate the impacts of a closed Drake Passage both with and without a Panama Seaway. We find that the climate response to a closed Drake Passage is relatively small when the Panama Seaway is absent, similar to prior studies, although the coupling to a dynamical atmosphere does increase the temperature change. However, with a Panama Seaway, closing Drake Passage has a much larger effect, due to the cessation of deep water formation in the northern hemisphere. Both gateways alter the transport of salt by ocean circulation, with the Panama Seaway allowing fresh Pacific water to be imported to the North Atlantic, and the Drake Passage preventing the flow of saline subtropical water to the circum-Antarctic, a flow that is particularly strong when the Panama Seaway is open. Thus, with a Panama Seaway and a closed Drake Passage, the Southern Ocean tends to be relatively salty, while the North Atlantic tends to be relatively fresh, such that the deep ocean is ventilated from the circum-Antarctic. Ensuing changes in the ocean heat transport drive a bi-polar shift of surface ocean temperatures, and the Intertropical Convergence Zone migrates toward the warmer southern hemisphere. The response of clouds to changes in surface ocean temperatures amplifies the climate response, resulting in temperature changes of up to 9 °C over Antarctica, even in the absence of land-ice feedbacks. These results emphasize the importance of tectonic gateways to the climate history of the Cenozoic, and support a role for ocean circulation changes in the glaciation of Antarctica.

Coral calcification and ocean acidification

USGS Publications Warehouse

Jokiel, Paul L.; Jury, Christopher P.; Kuffner, Ilsa B.

2016-01-01

Over 60 years ago, the discovery that light increased calcification in the coral plant-animal symbiosis triggered interest in explaining the phenomenon and understanding the mechanisms involved. Major findings along the way include the observation that carbon fixed by photosynthesis in the zooxanthellae is translocated to animal cells throughout the colony and that corals can therefore live as autotrophs in many situations. Recent research has focused on explaining the observed reduction in calcification rate with increasing ocean acidification (OA). Experiments have shown a direct correlation between declining ocean pH, declining aragonite saturation state (Ωarag), declining [CO32_] and coral calcification. Nearly all previous reports on OA identify Ωarag or its surrogate [CO32] as the factor driving coral calcification. However, the alternate “Proton Flux Hypothesis” stated that coral calcification is controlled by diffusion limitation of net H+ transport through the boundary layer in relation to availability of dissolved inorganic carbon (DIC). The “Two Compartment Proton Flux Model” expanded this explanation and synthesized diverse observations into a universal model that explains many paradoxes of coral metabolism, morphology and plasticity of growth form in addition to observed coral skeletal growth response to OA. It is now clear that irradiance is the main driver of net photosynthesis (Pnet), which in turn drives net calcification (Gnet), and alters pH in the bulk water surrounding the coral. Pnet controls [CO32] and thus Ωarag of the bulk water over the diel cycle. Changes in Ωarag and pH lag behind Gnet throughout the daily cycle by two or more hours. The flux rate Pnet, rather than concentration-based parameters (e.g., Ωarag, [CO3 2], pH and [DIC]:[H+] ratio) is the primary driver of Gnet. Daytime coral metabolism rapidly removes DIC from the bulk seawater. Photosynthesis increases the bulk seawater pH while providing the energy that drives calcification and increases in Gnet. These relationships result in a correlation between Gnet and Ωarag, with both parameters being variables dependent on Pnet. Consequently the correlation between Gnet and Ωarag varies widely between different locations and times depending on the relative metabolic contributions of various calcifying and photosynthesizing organisms and local rates of carbonate dissolution. High rates of H+ efflux continue for several hours following the mid-day Gnet peak suggesting that corals have difficulty in shedding waste protons as described by the Proton Flux Model. DIC flux (uptake) tracks Pnet and Gnet and drops off rapidly after the photosynthesis-calcification maxima, indicating that corals can cope more effectively with the problem of limited DIC supply compared to the problem of eliminating H+. Predictive models of future global changes in coral and coral reef growth based on oceanic Ωarag must include the influence of future changes in localized Pnet on Gnet as well as changes in rates of reef carbonate dissolution. The correlation between Ωarag and Gnet over the diel cycle is simply the result of increasing pH due to photosynthesis that shifts the CO2-carbonate system equilibria to increase [CO32] relative to the other DIC components of [HCO3] and [CO2]. Therefore Ωarag closely tracks pH as an effect of Pnet, which also drives changes in Gnet. Measurements of DIC flux and H+ flux are far more useful than concentrations in describing coral metabolism dynamics. Coral reefs are systems that exist in constant disequilibrium with the water column.

Quantifying trace element and isotope fluxes at the ocean–sediment boundary: a review

PubMed Central

Berelson, William M.; Severmann, Silke

2016-01-01

Quantifying fluxes of trace elements and their isotopes (TEIs) at the ocean's sediment–water boundary is a pre-eminent challenge to understand their role in the present, past and future ocean. There are multiple processes that drive the uptake and release of TEIs, and properties that determine their rates are unevenly distributed (e.g. sediment composition, redox conditions and (bio)physical dynamics). These factors complicate our efforts to find, measure and extrapolate TEI fluxes across ocean basins. GEOTRACES observations are unveiling the oceanic distributions of many TEIs for the first time. These data evidence the influence of the sediment–water boundary on many TEI cycles, and underline the fact that our knowledge of the source–sink fluxes that sustain oceanic distributions is largely missing. Present flux measurements provide low spatial coverage and only part of the empirical basis needed to predict TEI flux variations. Many of the advances and present challenges facing TEI flux measurements are linked to process studies that collect sediment cores, pore waters, sinking material or seawater in close contact with sediments. However, such sampling has not routinely been viable on GEOTRACES expeditions. In this article, we recommend approaches to address these issues: firstly, with an interrogation of emergent data using isotopic mass-balance and inverse modelling techniques; and secondly, by innovating pursuits of direct TEI flux measurements. We exemplify the value of GEOTRACES data with a new inverse model estimate of benthic Al flux in the North Atlantic Ocean. Furthermore, we review viable flux measurement techniques tailored to the sediment–water boundary. We propose that such activities are aimed at regions that intersect the GEOTRACES Science Plan on the basis of seven criteria that may influence TEI fluxes: sediment provenance, composition, organic carbon supply, redox conditions, sedimentation rate, bathymetry and the benthic nepheloid inventory. This article is part of the themed issue ‘Biological and climatic impacts of ocean trace element chemistry’. PMID:29035270

Can basal magma oceans generate magnetic fields?

NASA Astrophysics Data System (ADS)

Stegman, D. R.; Ziegler, L. B.; Davies, C.

2015-12-01

Earth's magnetic field is very old, with recent data now showing the field possibly extended back to 4.1 billion years ago (Tarduno et al., Science, 2015). Yet, based upon our current knowledge there are difficulties in sustained a core dynamo over most of Earth's history. Moreover, recent estimates of thermal and electrical conductivity of liquid iron at core conditions from mineral physics experiments indicate that adiabatic heat flux is approximately 15 TW, nearly 3 times larger than previously thought, exacerbating difficulties for driving a core dynamo by convective core cooling alone throughout Earth history. A long-lived basal magma ocean in the lowermost mantle has been proposed to exist in the early Earth, surviving perhaps into the Archean. While the modern, solid lower mantle is an electromagnetic insulator, electrical conductivities of silicate melts are known to be higher, though as yet they are unconstrained for lowermost mantle conditions. Here we explore the geomagnetic consequences of a basal magma ocean layer for a range of possible electrical conductivities. For the highest electrical conductivities considered, we find a basal magma ocean could be a primary dynamo source region. This would suggest the proposed three magnetic eras observed in paleomagnetic data originate from distinct sources for dynamo generation: from 4.5-2.45 Ga within a basal magma ocean, from 2.25-0.4 Ga within a superadiabatically cooled liquid core, and from 0.4-present within a quasi-adiabatic core that includes a solidifying inner core. We have extended this work by developing a new code, Dynamantle, which is a model with an entropy-based approach, similar to those commonly used in core dynamics models. We present new results using this code to assess the conditions under which basal magma oceans can generate positive ohmic dissipation. This is more generally useful than just considering the early Earth, but also for many silicate exoplanets in which basal magma oceans are even more likely to exist.

Evolution of ocean-induced ice melt beneath Zachariæ Isstrøm, Northeast Greenland combining observations and an ocean general circulation model from 1978 to present

NASA Astrophysics Data System (ADS)

Cai, C.; Rignot, E. J.; Menemenlis, D.; Millan, R.; Bjørk, A. A.; Khan, S. A.; Charolais, A.

2017-12-01

Zachariæ Isstrøm, a major ice stream in northeast Greenland, lost a large fraction of its ice shelf during the last decade. We study the evolution of subaqueous melting of its floating section from 1978 to present. The ice shelf melt rate depends on thermal forcing from warm, salty, subsurface ocean waters of Atlantic origin (AW), the mixing of AW with fresh, buoyant subglacial discharge at the calving margin, and the shape of the sub-ice-shelf cavity. Subglacial discharge doubled as a result of enhanced ice sheet runoff caused by warmer air temperatures. Ocean thermal forcing has increased due to enhanced advection of AW. Using an Eulerian method, MEaSUREs ice velocity, Operation IceBridge (OIB) ice thickness, and RACMO2.3 surface balance data, we evaluate the ice shelf melt rate in 1978, 1999 and 2010. The melt rate doubled from 1999 to 2010. Using a Lagrangian method with World View imagery, we map the melt rate in detail from 2011 to 2016. We compare the results with 2D simulations from the Massachusetts Institute of Technology general circulation model (MITgcm), at a high spatial resolution (20-m horizontal and 40-m vertical grid spacing), using OIB ice thickness and sub-ice-shelf cavity for years 1978, 1996, 2010 and 2011, combined with in-situ ocean temperature/salinity data from Ocean Melting Greenland (OMG) 2017. We find that winter melt rates are 2 3 times smaller than summer rates and melt rates increase by one order magnitude during the transition from ice shelf termination to near-vertical calving wall termination. As the last remaining bits of floating ice shelf disappear, ice-ocean interaction will therefore play an increasing role in driving the glacier retreat into its marine-based basin. This work was performed under a contract with NASA Cryosphere Program at UC Irvine and Caltech's Jet Propulsion Laboratory.

Transition of R&D into Operations at Fleet Numerical Meteorology and Oceanography Center

NASA Astrophysics Data System (ADS)

Clancy, R. M.

2006-12-01

The U.S. Navy's Fleet Numerical Meteorology and Oceanography Center (FNMOC) plays a significant role in the National capability for operational weather and ocean prediction through its operation of sophisticated global and regional meteorological and oceanographic models, extending from the top of the atmosphere to the bottom of the ocean. FNMOC uniquely satisfies the military's requirement for a global operational weather prediction capability based on software certified to DoD Information Assurance standards and operated in a secure classified computer environment protected from outside intrusion by DoD certified firewalls. FNMOC operates around-the-clock, 365 days per year and distributes products to military and civilian users around the world, both ashore and afloat, through a variety of means. FNMOC's customers include all branches of the Department of Defense, other government organizations such as the National Weather Service, private companies, a number of colleges and universities, and the general public. FNMOC employs three primary models, the Navy Operational Global Atmospheric Prediction System (NOGAPS), the Coupled Ocean/Atmosphere Mesoscale Prediction System (COAMPS), and the WaveWatch III model (WW3), along with a number of specialized models and related applications. NOGAPS is a global weather model, driving nearly all other FNMOC models and applications in some fashion. COAMPS is a high- resolution regional model that has proved to be particularly valuable for forecasting weather and ocean conditions in highly complex coastal areas. WW3 is a state-of-the-art ocean wave model that is employed both globally and regionally in support of a wide variety of naval operations. Other models support and supplement the main models with predictions of ocean thermal structure, ocean currents, sea-ice characteristics, and other data. Fleet Numerical operates at the leading edge of science and technology, and benefits greatly from collocation with its supporting R&D activity, the Marine Meteorology Division of the Naval Research Laboratory (NRL Code 7500). NRL Code 7500 is a world-class research organization, with focus on weather-related support for the warfighter. Fleet Numerical and NRL Code 7500 share space, data, software and computer systems, and together represent one of the largest concentrations of weather-related intellectual capital in the nation. As documented, for example, by the Board on Atmospheric Sciences and Climate (BASC) of the National Research Council, investment in R&D is crucial for maintaining state-of-the-art operational Numerical Weather Prediction (NWP) capabilities (see BASC, 1998). And collocation and close cooperation between research and operations, such as exists between NRL Code 7500 and Fleet Numerical, is the optimum arrangement for transitioning R&D quickly and cost-effectively into new and improved operational weather prediction capabilities.

Exploring the Circulation Dynamics of Mississippi Sound and Bight Using the CONCORDE Synthesis Model

NASA Astrophysics Data System (ADS)

Pan, C.; Dinniman, M. S.; Fitzpatrick, P. J.; Lau, Y.; Cambazoglu, M. K.; Parra, S. M.; Hofmann, E. E.; Dzwonkowski, B.; Warner, S. J.; O'Brien, S. J.; Dykstra, S. L.; Wiggert, J. D.

2017-12-01

As part of the modeling effort of the GOMRI (Gulf of Mexico Research Initiative)-funded CONCORDE consortium, a high resolution ( 400 m) regional ocean model is implemented for the Mississippi (MS) Sound and Bight. The model is based on the Coupled Ocean Atmosphere Wave Sediment Transport Modeling System (COAWST), with initial and lateral boundary conditions drawn from data assimilative 3-day forecasts of the 1km-resolution Gulf of Mexico Navy Coastal Ocean Model (GOM-NCOM). The model initiates on 01/01/2014 and runs for 3 years. The model results are validated with available remote sensing data and with CONCORDE's moored and ship-based in-situ observations. Results from a three-year simulation (2014-2016) show that ocean circulation and water properties of the MS Sound and Bight are sensitive to meteorological forcing. A low resolution surface forcing, drawn from the North America Regional Reanalysis (NARR), and a high resolution forcing, called CONCORDE Meteorological Analysis (CMA) ) that resolves the diurnal sea breeze, are used to drive the model to examine the sensitivity of the circulation to surface forcing. The model responses to the low resolution NARR forcing and to the high resolution CMA are compared in detail for the CONCORDE Fall and Spring field campaigns when contemporaneous in situ data are available, with a focus on how simulated exchanges between MS Sound and MS Bight are impacted. In most cases, the model shows higher simulation skill when it is driven by CMA. Freshwater plumes of the MS River, MS Sound and Mobile Bay influence the shelf waters of the MS Bight in terms of material budget and dynamics. Drifters and dye experiments near Mobile Bay demonstrate that material exchanges between Mobile Bay and the Sound, and between the Sound and Bight, are sensitive to the wind strength and direction. A model - data comparison targeting the Mobile Bay plume suggests that under both northerly and southerly wind conditions the model is capable of simulating the variation of the plume in terms of velocity, plume extent, heat and salt budgets.

North Tropical Atlantic Climate Variability and Model Biases

NASA Astrophysics Data System (ADS)

Yang, Y.

2017-12-01

Remote forcing from El Niño-Southern Oscillation (ENSO) and local ocean-atmosphere feedback are important for climate variability over the North Tropical Atlantic. These two factors are extracted by the ensemble mean and inter-member difference of a 10-member Pacific Ocean-Global Atmosphere (POGA) experiment, in which sea surface temperatures (SSTs) are restored to the observed anomalies over the tropical Pacific but fully coupled to the atmosphere elsewhere. POGA reasonably captures main features of observed North Tropical Atlantic variability. ENSO forced and local North Tropical Atlantic modes (NTAMs) develop with wind-evaporation-SST feedback, explaining one third and two thirds of total variance respectively. Notable biases, however, exist. The seasonality of the simulated NTAM is delayed by one month, due to the late development of the North Atlantic Oscillation (NAO) in the model. A spurious band of enhanced sea surface temperature (SST) variance (SBEV) is identified over the northern equatorial Atlantic in POGA and 14 out of 23 CMIP5 models. The SBEV is especially pronounced in boreal spring and due to the combined effect of both anomalous atmospheric thermal forcing and oceanic vertical upwelling. While the tropical North Atlantic variability is only weakly correlated with the Atlantic Zonal Mode (AZM) in observations, the SBEV in CMIP5 produces conditions that drive and intensify the AZM variability via triggering the Bjerknes feedback. This partially explains why AZM is strong in some CMIP5 models even though the equatorial cold tongue and easterly trades are biased low.

Interhemispheric gradient of atmospheric radiocarbon reveals natural variability of Southern Ocean winds

NASA Astrophysics Data System (ADS)

Rodgers, K. B.; Fletcher, S. E. M.; Bianchi, D.; Beaulieu, C.; Galbraith, E. D.; Gnanadesikan, A.; Hogg, A. G.; Iudicone, D.; Lintner, B.; Naegler, T.; Reimer, P. J.; Sarmiento, J. L.; Slater, R. D.

2011-01-01

Tree ring Δ14C data (Reimer et al., 2004; McCormac et al., 2004) indicate that atmospheric Δ14C varied on multi-decadal to centennial timescales, in both hemispheres, over the pre-industrial period AD 950-1830. Although the Northern and Southern Hemispheric Δ14C records display similar variability, it is difficult from these data alone to distinguish between variations driven by 14CO2 production in the upper atmosphere (Stuiver, 1980) and exchanges between carbon reservoirs (Siegenthaler, 1980). Here we consider rather the Interhemispheric Gradient in atmospheric Δ14C as revealing of the background pre-bomb air-sea Disequilbrium Flux between 14CO2 and CO2. As the global maximum of the Disequilibrium Flux is squarely centered in the open ocean regions of the Southern Ocean, relatively modest perturbations to the winds over this region drive significant perturbations to the Interhemispheric Gradient. The analysis presented here implies that changes to Southern Ocean windspeeds are likely a main driver of the observed variability in the Interhemispheric Gradient over 950-1830, and further, that this variability may be larger than the Southern Ocean wind trends that have been reported for recent decades (notably 1980-2004). This interpretation also implies a significant weakening of the winds over the Southern Ocean within a few decades of AD 1375, associated with the transition between the Medieval Climate Anomaly and the Little Ice Age. The driving forces that could have produced such a shift in the winds remain unkown.

Near 7-day response of ocean bottom pressure to atmospheric surface pressure and winds in the northern South China Sea

NASA Astrophysics Data System (ADS)

Zhang, Kun; Zhu, Xiao-Hua; Zhao, Ruixiang

2018-02-01

Ocean bottom pressures, observed by five pressure-recording inverted echo sounders (PIESs) from October 2012 to July 2014, exhibit strong near 7-day variability in the northern South China Sea (SCS) where long-term in situ bottom pressure observations are quite sparse. This variability was strongest in October 2013 during the near two years observation period. By joint analysis with European Center for Medium-Range Weather Forecasts (ECMWF) data, it is shown that the near 7-day ocean bottom pressure variability is closely related to the local atmospheric surface pressure and winds. Within a period band near 7 days, there are high coherences, exceeding 95% significance level, of observed ocean bottom pressure with local atmospheric surface pressure and with both zonal and meridional components of the wind. Ekman pumping/suction caused by the meridional component of the wind in particular, is suggested as one driving mechanism. A Kelvin wave response to the near 7-day oscillation would propagate down along the continental slope, observed at the Qui Nhon in the Vietnam. By multiple and partial coherence analyses, we find that local atmospheric surface pressure and Ekman pumping/suction show nearly equal influence on ocean bottom pressure variability at near 7-day periods. A schematic diagram representing an idealized model gives us a possible mechanism to explain the relationship between ocean bottom pressure and local atmospheric forcing at near 7-day periods in the northern SCS.

Global biogeography and evolution of Cuvierina pteropods.

PubMed

Burridge, Alice K; Goetze, Erica; Raes, Niels; Huisman, Jef; Peijnenburg, Katja T C A

2015-03-12

Shelled pteropods are planktonic gastropods that are potentially good indicators of the effects of ocean acidification. They also have high potential for the study of zooplankton evolution because they are metazoan plankton with a good fossil record. We investigated phenotypic and genetic variation in pteropods belonging to the genus Cuvierina in relation to their biogeographic distribution across the world's oceans. We aimed to assess species boundaries and to reconstruct their evolutionary history. We distinguished six morphotypes based on geometric morphometric analyses of shells from 926 museum and 113 fresh specimens. These morphotypes have distinct geographic distributions across the Atlantic, Pacific and Indian oceans, and belong to three major genetic clades based on COI and 28S DNA sequence data. Using a fossil-calibrated phylogeny, we estimated that these clades separated in the Late Oligocene and Early to Middle Miocene. We found evidence for ecological differentiation among all morphotypes based on ecological niche modelling with sea surface temperature, salinity and phytoplankton biomass as primary determinants. Across all analyses, we found highly congruent patterns of differentiation suggesting species level divergences between morphotypes. However, we also found distinct morphotypes (e.g. in the Atlantic Ocean) that were ecologically, but not genetically differentiated. Given the distinct ecological and phenotypic specializations found among both described and undescribed Cuvierina taxa, they may not respond equally to future ocean changes and may not be equally sensitive to ocean acidification. Our findings support the view that ecological differentiation may be an important driving force in the speciation of zooplankton.

The Coastal and Marine Geology Program of the U.S. Geological Survey

USGS Publications Warehouse

Williams, S. Jeffress

1997-01-01

Nearly half of all Americans live within an hour's drive of an ocean, the Gulf of Mexico, or the Great Lakes. The U.S. coastal oceans are an economically vital transportation, commercial and recreational resource. They provide food, energy, and minerals for the entire Nation: on a global scale, they harbor critical habitat for important animal and plant species.

Modelling sea ice formation in the Terra Nova Bay polynya

NASA Astrophysics Data System (ADS)

Sansiviero, M.; Morales Maqueda, M. Á.; Fusco, G.; Aulicino, G.; Flocco, D.; Budillon, G.

2017-02-01

Antarctic sea ice is constantly exported from the shore by strong near surface winds that open leads and large polynyas in the pack ice. The latter, known as wind-driven polynyas, are responsible for significant water mass modification due to the high salt flux into the ocean associated with enhanced ice growth. In this article, we focus on the wind-driven Terra Nova Bay (TNB) polynya, in the western Ross Sea. Brine rejected during sea ice formation processes that occur in the TNB polynya densifies the water column leading to the formation of the most characteristic water mass of the Ross Sea, the High Salinity Shelf Water (HSSW). This water mass, in turn, takes part in the formation of Antarctic Bottom Water (AABW), the densest water mass of the world ocean, which plays a major role in the global meridional overturning circulation, thus affecting the global climate system. A simple coupled sea ice-ocean model has been developed to simulate the seasonal cycle of sea ice formation and export within a polynya. The sea ice model accounts for both thermal and mechanical ice processes. The oceanic circulation is described by a one-and-a-half layer, reduced gravity model. The domain resolution is 1 km × 1 km, which is sufficient to represent the salient features of the coastline geometry, notably the Drygalski Ice Tongue. The model is forced by a combination of Era Interim reanalysis and in-situ data from automatic weather stations, and also by a climatological oceanic dataset developed from in situ hydrographic observations. The sensitivity of the polynya to the atmospheric forcing is well reproduced by the model when atmospheric in situ measurements are combined with reanalysis data. Merging the two datasets allows us to capture in detail the strength and the spatial distribution of the katabatic winds that often drive the opening of the polynya. The model resolves fairly accurately the sea ice drift and sea ice production rates in the TNB polynya, leading to realistic polynya extent estimates. The model-derived polynya extent has been validated by comparing the modelled sea ice concentration against MODIS high resolution satellite images, confirming that the model is able to reproduce reasonably well the TNB polynya evolution in terms of both shape and extent.

Influences of Ocean Thermohaline Stratification on Arctic Sea Ice

NASA Astrophysics Data System (ADS)

Toole, J. M.; Timmermans, M.-L.; Perovich, D. K.; Krishfield, R. A.; Proshutinsky, A.; Richter-Menge, J. A.

2009-04-01

The Arctic Ocean's surface mixed layer constitutes the dynamical and thermodynamical link between the sea ice and the underlying waters. Wind stress, acting directly on the surface mixed layer or via wind-forced ice motion, produce surface currents that can in turn drive deep ocean flow. Mixed layer temperature is intimately related to basal sea ice growth and melting. Heat fluxes into or out of the surface mixed layer can occur at both its upper and lower interfaces: the former via air-sea exchange at leads and conduction through the ice, the latter via turbulent mixing and entrainment at the layer base. Variations in Arctic Ocean mixed layer properties are documented based on more than 16,000 temperature and salinity profiles acquired by Ice-Tethered Profilers since summer 2004 and analyzed in conjunction with sea ice observations from Ice Mass Balance Buoys and atmospheric heat flux estimates. Guidance interpreting the observations is provided by a one-dimensional ocean mixed layer model. The study focuses attention on the very strong density stratification about the mixed layer base in the Arctic that, in regions of sea ice melting, is increasing with time. The intense stratification greatly impedes mixed layer deepening by vertical convection and shear mixing, and thus limits the flux of deep ocean heat to the surface that could influence sea ice growth/decay. Consistent with previous work, this study demonstrates that the Arctic sea ice is most sensitive to changes in ocean mixed layer heat resulting from fluxes across its upper (air-sea and/or ice-water) interface.

Seasonal and Interannual Variations of Sea Ice Mass Balance From the Central Arctic to the Greenland Sea

NASA Astrophysics Data System (ADS)

Lei, Ruibo; Cheng, Bin; Heil, Petra; Vihma, Timo; Wang, Jia; Ji, Qing; Zhang, Zhanhai

2018-04-01

The seasonal evolution of sea ice mass balance between the Central Arctic and Fram Strait, as well as the underlying driving forces, remain largely unknown because of a lack of observations. In this study, two and three buoys were deployed in the Central Arctic during the summers of 2010 and 2012, respectively. It was established that basal ice growth commenced between mid-October and early December. Annual basal ice growth, ranging from 0.21 to 1.14 m, was determined mainly by initial ice thickness, air temperature, and oceanic heat flux during winter. An analytic thermodynamic model indicated that climate warming reduces the winter growth rate of thin ice more than for thick ice because of the weak thermal inertia of the former. Oceanic heat flux during the freezing season was 2-4 W m-2, which accounted for 18-31% of the basal ice energy balance. We identified two mechanisms that modified the oceanic heat flux, i.e., solar energy absorbed by the upper ocean during summer, and interaction with warm waters south of Fram Strait; the latter resulted in basal ice melt, even in winter. In summer 2010, ice loss in the Central Arctic was considerable, which led to increased oceanic heat flux into winter and delayed ice growth. The Transpolar Drift Stream was relatively weak in summer 2013. This reduced sea ice advection out of the Arctic Ocean, and it restrained ice melt because of the cool atmospheric conditions, weakened albedo feedback, and relatively small oceanic heat flux in the north.

Entorhinal Cortical Ocean Cells Encode Specific Contexts and Drive Context-Specific Fear Memory

PubMed Central

Kitamura, Takashi; Sun, Chen; Martin, Jared; Kitch, Lacey J; Schnitzer, Mark J; Tonegawa, Susumu

2016-01-01

Summary Forming distinct representations and memories of multiple contexts and episodes is thought to be a crucial function of the hippocampal-entorhinal cortical network. The hippocampal dentate gyrus (DG) and CA3 are known to contribute to these functions but the role of the entorhinal cortex (EC) is poorly understood. Here, we show that Ocean cells, excitatory stellate neurons in the medial EC layer II projecting into DG and CA3, rapidly form a distinct representation of a novel context and drive context-specific activation of downstream CA3 cells as well as context-specific fear memory. In contrast, Island cells, excitatory pyramidal neurons in the medial EC layer II projecting into CA1, are indifferent to context-specific encoding or memory. On the other hand, Ocean cells are dispensable for temporal association learning, for which Island cells are crucial. Together, the two excitatory medial EC layer II inputs to the hippocampus have complementary roles in episodic memory. PMID:26402611

Isolating the atmospheric circulation response to Arctic sea-ice loss in the coupled climate system

NASA Astrophysics Data System (ADS)

Kushner, P. J.; Blackport, R.

2016-12-01

In the coupled climate system, projected global warming drives extensive sea-ice loss, but sea-ice loss drives warming that amplifies and can be confounded with the global warming process. This makes it challenging to cleanly attribute the atmospheric circulation response to sea-ice loss within coupled earth-system model (ESM) simulations of greenhouse warming. In this study, many centuries of output from coupled ocean/atmosphere/land/sea-ice ESM simulations driven separately by sea-ice albedo reduction and by projected greenhouse-dominated radiative forcing are combined to cleanly isolate the hemispheric scale response of the circulation to sea-ice loss. To isolate the sea-ice loss signal, a pattern scaling approach is proposed in which the local multidecadal mean atmospheric response is assumed to be separately proportional to the total sea-ice loss and to the total low latitude ocean surface warming. The proposed approach estimates the response to Arctic sea-ice loss with low latitude ocean temperatures fixed and vice versa. The sea-ice response includes a high northern latitude easterly zonal wind response, an equatorward shift of the eddy driven jet, a weakening of the stratospheric polar vortex, an anticyclonic sea level pressure anomaly over coastal Eurasia, a cyclonic sea level pressure anomaly over the North Pacific, and increased wintertime precipitation over the west coast of North America. Many of these responses are opposed by the response to low-latitude surface warming with sea ice fixed. However, both sea-ice loss and low latitude surface warming act in concert to reduce storm track strength throughout the mid and high latitudes. The responses are similar in two related versions of the National Center for Atmospheric Research earth system models, apart from the stratospheric polar vortex response. Evidence is presented that internal variability can easily contaminate the estimates if not enough independent climate states are used to construct them.

Atlantic-induced pan-tropical climate change over the past three decades

NASA Astrophysics Data System (ADS)

Li, Xichen; Xie, Shang-Ping; Gille, Sarah T.; Yoo, Changhyun

2016-03-01

During the past three decades, tropical sea surface temperature (SST) has shown dipole-like trends, with warming over the tropical Atlantic and Indo-western Pacific but cooling over the eastern Pacific. Competing hypotheses relate this cooling, identified as a driver of the global warming hiatus, to the warming trends in either the Atlantic or Indian Ocean. However, the mechanisms, the relative importance and the interactions between these teleconnections remain unclear. Using a state-of-the-art climate model, we show that the Atlantic plays a key role in initiating the tropical-wide teleconnection, and the Atlantic-induced anomalies contribute ~55-75% of the tropical SST and circulation changes during the satellite era. The Atlantic warming drives easterly wind anomalies over the Indo-western Pacific as Kelvin waves and westerly anomalies over the eastern Pacific as Rossby waves. The wind changes induce an Indo-western Pacific warming through the wind-evaporation-SST effect, and this warming intensifies the La Niña-type response in the tropical Pacific by enhancing the easterly trade winds and through the Bjerknes ocean dynamical processes. The teleconnection develops into a tropical-wide SST dipole pattern. This mechanism, supported by observations and a hierarchy of climate models, reveals that the tropical ocean basins are more tightly connected than previously thought.

Coastal development and precipitation drive pathogen flow from land to sea: evidence from a Toxoplasma gondii and felid host system

PubMed Central

VanWormer, Elizabeth; Carpenter, Tim E; Singh, Purnendu; Shapiro, Karen; Wallender, Wesley W.; Conrad, Patricia A.; Largier, John L.; Maneta, Marco P.; Mazet, Jonna A. K.

2016-01-01

Rapidly developing coastal regions face consequences of land use and climate change including flooding and increased sediment, nutrient, and chemical runoff, but these forces may also enhance pathogen runoff, which threatens human, animal, and ecosystem health. Using the zoonotic parasite Toxoplasma gondii in California, USA as a model for coastal pathogen pollution, we examine the spatial distribution of parasite runoff and the impacts of precipitation and development on projected pathogen delivery to the ocean. Oocysts, the extremely hardy free-living environmental stage of T. gondii shed in faeces of domestic and wild felids, are carried to the ocean by freshwater runoff. Linking spatial pathogen loading and transport models, we show that watersheds with the highest levels of oocyst runoff align closely with regions of increased sentinel marine mammal T. gondii infection. These watersheds are characterized by higher levels of coastal development and larger domestic cat populations. Increases in coastal development and precipitation independently raised oocyst delivery to the ocean (average increases of 44% and 79%, respectively), but dramatically increased parasite runoff when combined (175% average increase). Anthropogenic changes in landscapes and climate can accelerate runoff of diverse pathogens from terrestrial to aquatic environments, influencing transmission to people, domestic animals, and wildlife. PMID:27456911

Coastal development and precipitation drive pathogen flow from land to sea: evidence from a Toxoplasma gondii and felid host system.

PubMed

VanWormer, Elizabeth; Carpenter, Tim E; Singh, Purnendu; Shapiro, Karen; Wallender, Wesley W; Conrad, Patricia A; Largier, John L; Maneta, Marco P; Mazet, Jonna A K

2016-07-26

Rapidly developing coastal regions face consequences of land use and climate change including flooding and increased sediment, nutrient, and chemical runoff, but these forces may also enhance pathogen runoff, which threatens human, animal, and ecosystem health. Using the zoonotic parasite Toxoplasma gondii in California, USA as a model for coastal pathogen pollution, we examine the spatial distribution of parasite runoff and the impacts of precipitation and development on projected pathogen delivery to the ocean. Oocysts, the extremely hardy free-living environmental stage of T. gondii shed in faeces of domestic and wild felids, are carried to the ocean by freshwater runoff. Linking spatial pathogen loading and transport models, we show that watersheds with the highest levels of oocyst runoff align closely with regions of increased sentinel marine mammal T. gondii infection. These watersheds are characterized by higher levels of coastal development and larger domestic cat populations. Increases in coastal development and precipitation independently raised oocyst delivery to the ocean (average increases of 44% and 79%, respectively), but dramatically increased parasite runoff when combined (175% average increase). Anthropogenic changes in landscapes and climate can accelerate runoff of diverse pathogens from terrestrial to aquatic environments, influencing transmission to people, domestic animals, and wildlife.

The role of Southern Ocean mixing and upwelling in glacial-interglacial atmospheric CO2 change

NASA Astrophysics Data System (ADS)

Watson, Andrew J.; Naveira Garabato, Alberto C.

2006-02-01

Decreased ventilation of the Southern Ocean in glacial time is implicated in most explanations of lower glacial atmospheric CO2. Today, the deep (>2000 m) ocean south of the Polar Front is rapidly ventilated from below, with the interaction of deep currents with topography driving high mixing rates well up into the water column. We show from a buoyancy budget that mixing rates are high in all the deep waters of the Southern Ocean. Between the surface and ~2000 m depth, water is upwelled by a residual meridional overturning that is directly linked to buoyancy fluxes through the ocean surface. Combined with the rapid deep mixing, this upwelling serves to return deep water to the surface on a short time scale. We propose two new mechanisms by which, in glacial time, the deep Southern Ocean may have been more isolated from the surface. Firstly, the deep ocean appears to have been more stratified because of denser bottom water resulting from intense sea ice formation near Antarctica. The greater stratification would have slowed the deep mixing. Secondly, subzero atmospheric temperatures may have meant that the present-day buoyancy flux from the atmosphere to the ocean surface was reduced or reversed. This in turn would have reduced or eliminated the upwelling (contrary to a common assumption, upwelling is not solely a function of the wind stress but is coupled to the air-sea buoyancy flux too). The observed very close link between Antarctic temperatures and atmospheric CO2 could then be explained as a natural consequence of the connection between the air-sea buoyancy flux and upwelling in the Southern Ocean, if slower ventilation of the Southern Ocean led to lower atmospheric CO2. Here we use a box model, similar to those of previous authors, to show that weaker mixing and reduced upwelling in the Southern Ocean can explain the low glacial atmospheric CO2 in such a formulation.

Numerical simulation and prediction of coastal ocean circulation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chen, P.

1992-01-01

Numerical simulation and prediction of coastal ocean circulation have been conducted in three cases. 1. A process-oriented modeling study is conducted to study the interaction of a western boundary current (WBC) with coastal water, and its responses to upstream topographic irregularities. It is hypothesized that the interaction of propagating WBC frontal waves and topographic Rossby waves are responsible for upstream variability. 2. A simulation of meanders and eddies in the Norwegian Coastal Current (NCC) for February and March of 1988 is conducted with a newly developed nested dynamic interactive model. The model employs a coarse-grid, large domain to account formore » non-local forcing and a fine-grid nested domain to resolve meanders and eddies. The model is forced by wind stresses, heat fluxes and atmospheric pressure corresponding Feb/March of 1988, and accounts for river/fjord discharges, open ocean inflow and outflow, and M[sub 2] tides. The simulation reproduced fairly well the observed circulation, tides, and salinity features in the North Sea, Norwegian Trench and NCC region in the large domain and fairly realistic meanders and eddies in the NCC in the nested region. 3. A methodology for practical coastal ocean hindcast/forecast is developed, taking advantage of the disparate time scales of various forcing and considering wind to be the dominant factor in affecting density fluctuation in the time scale of 1 to 10 days. The density field obtained from a prognostic simulation is analyzed by the empirical orthogonal function method (EOF), and correlated with the wind; these information are then used to drive a circulation model which excludes the density calculation. The method is applied to hindcast the circulation in the New York Bight for spring and summer season of 1988. The hindcast fields compare favorably with the results obtained from the prognostic circulation model.« less

Surface Buoyancy Fluxes and the Strength of the Subpolar Gyre

NASA Astrophysics Data System (ADS)

Hogg, A. M.; Gayen, B.

2017-12-01

Midlatitude ocean gyres have long been considered to be driven by the mechanical wind stress on the ocean's surface (strictly speaking, the potential vorticity input from wind stress curl). However, surface buoyancy forcing (i.e. heating/cooling or freshening/salinification) also modifies the potential vorticity at the surface. Here, we present a simple argument to demonstrate that ocean gyres may (in principle) be driven by surface buoyancy forcing. This argument is derived in two ways: A Direct Numerical Simulation, driven purely by buoyancy forcing, which generates strong nonlinear gyers in the absence of wind stress; and A series of idealised eddy-resolving numerical ocean model simulations, in which wind stress and buoyancy flux are varied independently and together, are used to understand the relative importance of these two types of forcing. In these simulations, basin-scale gyres and western boundary currents with realistic magnitudes, remain even in the absence of mechanical forcing by surface wind stress. These results support the notion that surface buoyancy forcing can reorganise the potential vorticity in the ocean in such a way as to drive basin-scale gyres. The role of buoyancy is stronger in the subpolar gyre than in the subtropical gyre. We infer that surface buoyancy fluxes are likely to play a contributing role in governing the strength, variability and predictability of the North Atlantic subpolar gyre.

Molybdenum drawdown during Cretaceous Oceanic Anoxic Event 2

NASA Astrophysics Data System (ADS)

Goldberg, Tatiana; Poulton, Simon W.; Wagner, Thomas; Kolonic, Sadat F.; Rehkämper, Mark

2016-04-01

During the Cretaceous greenhouse, episodes of widespread ocean deoxygenation were associated with globally occurring events of black shale deposition. Possibly the most pronounced of these oceanic anoxic events (OAE's) was the Cenomanian-Turonian OAE2 (∼94 Ma). However, although certain redox sensitive trace metals tend to be preferentially sequestered in sediments deposited under anoxic conditions, with Mo drawdown being specifically prone to euxinic settings, these elements are generally somewhat depleted in sediments deposited during OAE2. To understand the driving factors responsible for this depleted trace metal drawdown, we have studied a low latitude section from the proto-North Atlantic Ocean (Tarfaya S57), where existing biomarker and iron-sulphur data point to a dominantly euxinic water column, with periodic transitions to ferruginous (Fe-rich) water column conditions. We utilise a variety of redox proxies (Fe-speciation, redox sensitive trace metals and Mo isotopes), which, in combination, allows us to evaluate the detailed nature of ocean redox conditions and hence controls on trace metal drawdown. The results suggest that seawater δ98Mo values may have ranged between ∼0.6 and 1.1‰ during OAE2, likely connected to changes in the local Mo reservoir as a consequence of low and probably heterogeneous concentrations of Mo in the ocean. The very low Mo/TOC ratios at Tarfaya and elsewhere in the proto-North Atlantic may support a model in which deep-water circulation was partially restricted within and between the North Atlantic and other ocean basins. We propose that the combination of a low and possibly heterogeneous δ98Mo of seawater Mo, together with low Mo/TOC ratios, points to a large decrease in the global oceanic Mo reservoir during OAE2, reflecting a major global scale increase in Mo drawdown under persistent euxinic conditions.

76 FR 62408 - Ocean Transportation Intermediary License; Reissuance

Federal Register 2010, 2011, 2012, 2013, 2014

2011-10-07

.... 019746N Carmen Cargo August 25, 2011. Express Inc., 2130 SW. 58th Way, West Park, FL 33023. 021094F Amid Logistics, May 23, 2011. LLC, 10 Florida Park Drive, N., Suite D-1A, Palm Coast, FL 32137. 021781N T.V.L..., Incorporated dba U.S. Northwest Express dba USNW Express, 5150 Village Park Drive, SE., Suite 100, Bellevue, WA...

Seasonal-to-Interannual Variability in Antarctic Sea-Ice Dynamics, and Its Impact on Surface Fluxes and Water Mass Production

NASA Technical Reports Server (NTRS)

Drinkwater, Mark R.

1999-01-01

Strong seasonal and interannual signals in Antarctic bottom-water outflow remain unexplained yet are highly correlated with anomalies in net sea-ice growth in coastal polynyas. The mechanisms responsible for driving salination and replenishment and rejuvenation of the dense shelf "source" waters likely also generate pulses of bottom water outflow. The objective of this research is to investigate time-scales of variability in the dynamics of sea-ice in the Southern Ocean in order to determine the primary sites for production of dense shelf waters. We are using a merged satellite/buoy sea-ice motion data set for the period 1978-present day to compute the dynamics of opening and closing of coastal polynyas over the continental shelf. The Ocean Circulation and Climate Advanced Model (OCCAM) ocean general circulation model with coupled sea-ice dynamics is presently forced using National Center for Environmental Prediction (NCEP) data to simulate fluxes and the salination impact of the ocean shelf regions. This work is relevant in the context of measuring the influence of polar sea-ice dynamics upon polar ocean characteristics, and thereby upon global thermohaline ocean circulation. Interannual variability in simulated net freezing rate in the Southern Weddell Sea is shown for the period 1986-1993. There is a pronounced maximum of ice production in 1988 and minimum in 1991 in response to anomalies in equatorward meridional wind velocity. This follows a similar approximate 8-year interannual cycle in Sea Surface Temperature (SST) and satellite-derived ice-edge anomalies reported elsewhere as the "Antarctic Circumpolar Wave." The amplitude of interannual fluctuations in annual net ice production are about 40% of the mean value, implying significant interannual variance in brine rejection and upper ocean heat loss. Southward anomalies in wind stress induce negative anomalies in open water production, which are observed in passive microwave satellite images. Thus, cycles of enhanced poleward wind stress reduce ice growth by compacting the ice along the coastline and closing open water in leads and polynyas. Model simulations confirm that years of low ice production, such as 1991, coincide with years of lower than normal bottom water outflow. Future plans include the assimilation of satellite ice concentrations and ice drift dynamics to more accurately constrain boundary conditions in the model.

Spaceborne studies of ocean circulation

NASA Technical Reports Server (NTRS)

Patzert, W. C.

1984-01-01

The history and near-term future of ocean remote sensing to study ocean circulation are examined. Seasat provided the first-ever global data sets of sea surface topography (altimeter) and marine winds (scatterometer) and laid the foundation for the next generation of satellite missions planned for the late 1980s. The future missions are the next generation of altimeter and scatterometer to be flown aboard TOPEX (TOPography EXperiment) and NROSS (Navy Remote Sensing System), respectively. The data from these satellites will be coordinated with measurements made at sea to determine the driving forces of ocean circulation and to study the oceans' role in climate variability. The significance of such studies to such matters as climatic changes, fisheries, commerce, waste disposal, and national defense is noted.

Charcoal evidence that rising atmospheric oxygen terminated Early Jurassic ocean anoxia

PubMed Central

Baker, Sarah J.; Hesselbo, Stephen P.; Lenton, Timothy M.; Duarte, Luís V.; Belcher, Claire M.

2017-01-01

The Toarcian Oceanic Anoxic Event (T-OAE) was characterized by a major disturbance to the global carbon(C)-cycle, and depleted oxygen in Earth's oceans resulting in marine mass extinction. Numerical models predict that increased organic carbon burial should drive a rise in atmospheric oxygen (pO2) leading to termination of an OAE after ∼1 Myr. Wildfire is highly responsive to changes in pO2 implying that fire-activity should vary across OAEs. Here we test this hypothesis by tracing variations in the abundance of fossil charcoal across the T-OAE. We report a sustained ∼800 kyr enhancement of fire-activity beginning ∼1 Myr after the onset of the T-OAE and peaking during its termination. This major enhancement of fire occurred across the timescale of predicted pO2 variations, and we argue this was primarily driven by increased pO2. Our study provides the first fossil-based evidence suggesting that fire-feedbacks to rising pO2 may have aided in terminating the T-OAE. PMID:28497785

Charcoal evidence that rising atmospheric oxygen terminated Early Jurassic ocean anoxia.

PubMed

Baker, Sarah J; Hesselbo, Stephen P; Lenton, Timothy M; Duarte, Luís V; Belcher, Claire M

2017-05-12

The Toarcian Oceanic Anoxic Event (T-OAE) was characterized by a major disturbance to the global carbon(C)-cycle, and depleted oxygen in Earth's oceans resulting in marine mass extinction. Numerical models predict that increased organic carbon burial should drive a rise in atmospheric oxygen (pO 2 ) leading to termination of an OAE after ∼1 Myr. Wildfire is highly responsive to changes in pO 2 implying that fire-activity should vary across OAEs. Here we test this hypothesis by tracing variations in the abundance of fossil charcoal across the T-OAE. We report a sustained ∼800 kyr enhancement of fire-activity beginning ∼1 Myr after the onset of the T-OAE and peaking during its termination. This major enhancement of fire occurred across the timescale of predicted pO 2 variations, and we argue this was primarily driven by increased pO 2 . Our study provides the first fossil-based evidence suggesting that fire-feedbacks to rising pO 2 may have aided in terminating the T-OAE.

The significance of parameter uncertainties for the prediction of offshore pile driving noise.

PubMed

Lippert, Tristan; von Estorff, Otto

2014-11-01

Due to the construction of offshore wind farms and its potential effect on marine wildlife, the numerical prediction of pile driving noise over long ranges has recently gained importance. In this contribution, a coupled finite element/wavenumber integration model for noise prediction is presented and validated by measurements. The ocean environment, especially the sea bottom, can only be characterized with limited accuracy in terms of input parameters for the numerical model at hand. Therefore the effect of these parameter uncertainties on the prediction of sound pressure levels (SPLs) in the water column is investigated by a probabilistic approach. In fact, a variation of the bottom material parameters by means of Monte-Carlo simulations shows significant effects on the predicted SPLs. A sensitivity analysis of the model with respect to the single quantities is performed, as well as a global variation. Based on the latter, the probability distribution of the SPLs at an exemplary receiver position is evaluated and compared to measurements. The aim of this procedure is to develop a model to reliably predict an interval for the SPLs, by quantifying the degree of uncertainty of the SPLs with the MC simulations.

Fifty Years of Water Cycle Change expressed in Ocean Salinity

NASA Astrophysics Data System (ADS)

Durack, P. J.; Wijffels, S.

2010-12-01

Using over 1.6 million profiles of salinity, potential temperature and density from historical archives and Argo, we derive the global field of linear change for ocean state properties over the period 1950-2008, taking care to minimise aliasing associated with seasonal and El Nino Southern Oscillation modes. We find large, robust and spatially coherent multi-decadal linear trends in ocean surface salinities. Increases are found in evaporation-dominated regions and freshening in precipitation-dominated regions. The spatial patterns of surface change strongly resemble the climatological mean surface salinity field, consistent with an amplification of the global water cycle. A robust amplification of the mean salinity pattern of 8% (to 200m depth) is found globally and 5-9% is found in each of the 3 key ocean basins. 20th century runs from the CMIP3 model suite support the relationship between amplified patterns of freshwater flux driving an amplified pattern of ocean surface salinity only in models that warm substantially. Models with volcanic aerosols show a diminished warming response and a corresponding weak response in ocean surface salinity change, which implies dampened changes to the global water cycle. The warming response represented in realistic (when compared to observations) 20th century simulations appear quite similar in their broad zonal patterns to those of the projected 21st century simulations, these projected runs being strongly forced by greenhouse gases. This pattern amplification is mostly absent from 20th century simulations which include volcanic forcing. While we confirm that global mean precipitation only weakly change with surface warming (2-3% K-1), the pattern amplification rate in both the freshwater flux and ocean salinity fields indicate larger responses. Our new observed salinity estimates suggest a change of between 8-16% K-1, close to, or greater than, the theoretical response described by the Clausius-Clapeyron relation. The underestimation of change patterns by the CMIP3 model suite is well documented in recent literature describing changes to the atmospheric and terrestrial arms of the global water cycle. These new observational ocean results add emphasis to the conclusion that the rate of observed changes in the 20th century are larger than CMIP3 models, and simplified physical theories predict. A) The 50-year linear surface salinity trend (pss/50-years). Contours every 0.25 pss are plotted in white. B) Ocean-atmosphere freshwater flux (m3 yr-1) averaged over 1980-1993 (Josey et al., 1998). Contours every 1 m3 yr-1 are in white. On both panels, the 1975 surface mean salinity is contoured black (contour interval 0.5 pss for thin lines, 1 for thick lines).

Contributions of Volcanic Carbon Emissions to Environmental Change at the Cretaceous-Paleogene and Paleocene-Eocene Boundaries: Observational and Theoretical Constraints

NASA Astrophysics Data System (ADS)

Zachos, J. C.; Penman, D. E.; Ridgwell, A.

2017-12-01

The terminations of both the Cretaceous Period (K-Pg) and Paleocene Epoch (P-E) coincided with episodes of extensive flood basalt/rift volcanism, the Deccan Traps (DT) and North Atlantic Igneous Province (NAIP), respectively. The latest radiometric data confirm that the main phases of magma extrusion of both DT and NAIP were concentrated over relatively short intervals (<<0.5 myr) further bolstering speculation on the role of volcanic C and other emissions in driving the observed environmental and biotic events of those terminations. Much of the speculation regarding C emissions has been derived from observations of changes in climate and/or ocean chemistry. Indeed, to drive detectable global warming and/or ocean acidification, C emissions would have to be significantly elevated over "typical" magmatic emission levels, thus requiring supplemental sources of C, most likely from intrusion driven combustion of organic matter and/or carbonate-rich crust. Here we compare marine geochemical records spanning both boundaries and with numerical models assess implications for C emissions and relations to the key environmental changes associated with each event. This assessment benefits from the recent development of high-fidelity (i.e., astronomically-tuned) proxy records of the climate and ocean carbon chemistry (e.g., SST, δ13C, pH) across both time intervals from globally distributed, stratigraphically complete marine sections. In the case of the K-Pg transition, the timing of changes in climate and ocean carbon chemistry along with other data indicate a comparatively inconsequential role of elevated C emissions on the major biotic event (i.e., extinction) marking that boundary. In contrast, with the P-E boundary, North Atlantic volcanism now appears to have been primary trigger/driver of climatic change, though positive feedbacks involving reduced C reservoirs (e.g., hydrates, permafrost) might have accelerated C emission rates at the onset of that event.

Chapter 1. Impacts of the oceans on climate change.

PubMed

Reid, Philip C; Fischer, Astrid C; Lewis-Brown, Emily; Meredith, Michael P; Sparrow, Mike; Andersson, Andreas J; Antia, Avan; Bates, Nicholas R; Bathmann, Ulrich; Beaugrand, Gregory; Brix, Holger; Dye, Stephen; Edwards, Martin; Furevik, Tore; Gangstø, Reidun; Hátún, Hjálmar; Hopcroft, Russell R; Kendall, Mike; Kasten, Sabine; Keeling, Ralph; Le Quéré, Corinne; Mackenzie, Fred T; Malin, Gill; Mauritzen, Cecilie; Olafsson, Jón; Paull, Charlie; Rignot, Eric; Shimada, Koji; Vogt, Meike; Wallace, Craig; Wang, Zhaomin; Washington, Richard

2009-01-01

The oceans play a key role in climate regulation especially in part buffering (neutralising) the effects of increasing levels of greenhouse gases in the atmosphere and rising global temperatures. This chapter examines how the regulatory processes performed by the oceans alter as a response to climate change and assesses the extent to which positive feedbacks from the ocean may exacerbate climate change. There is clear evidence for rapid change in the oceans. As the main heat store for the world there has been an accelerating change in sea temperatures over the last few decades, which has contributed to rising sea-level. The oceans are also the main store of carbon dioxide (CO2), and are estimated to have taken up approximately 40% of anthropogenic-sourced CO2 from the atmosphere since the beginning of the industrial revolution. A proportion of the carbon uptake is exported via the four ocean 'carbon pumps' (Solubility, Biological, Continental Shelf and Carbonate Counter) to the deep ocean reservoir. Increases in sea temperature and changing planktonic systems and ocean currents may lead to a reduction in the uptake of CO2 by the ocean; some evidence suggests a suppression of parts of the marine carbon sink is already underway. While the oceans have buffered climate change through the uptake of CO2 produced by fossil fuel burning this has already had an impact on ocean chemistry through ocean acidification and will continue to do so. Feedbacks to climate change from acidification may result from expected impacts on marine organisms (especially corals and calcareous plankton), ecosystems and biogeochemical cycles. The polar regions of the world are showing the most rapid responses to climate change. As a result of a strong ice-ocean influence, small changes in temperature, salinity and ice cover may trigger large and sudden changes in regional climate with potential downstream feedbacks to the climate of the rest of the world. A warming Arctic Ocean may lead to further releases of the potent greenhouse gas methane from hydrates and permafrost. The Southern Ocean plays a critical role in driving, modifying and regulating global climate change via the carbon cycle and through its impact on adjacent Antarctica. The Antarctic Peninsula has shown some of the most rapid rises in atmospheric and oceanic temperature in the world, with an associated retreat of the majority of glaciers. Parts of the West Antarctic ice sheet are deflating rapidly, very likely due to a change in the flux of oceanic heat to the undersides of the floating ice shelves. The final section on modelling feedbacks from the ocean to climate change identifies limitations and priorities for model development and associated observations. Considering the importance of the oceans to climate change and our limited understanding of climate-related ocean processes, our ability to measure the changes that are taking place are conspicuously inadequate. The chapter highlights the need for a comprehensive, adequately funded and globally extensive ocean observing system to be implemented and sustained as a high priority. Unless feedbacks from the oceans to climate change are adequately included in climate change models, it is possible that the mitigation actions needed to stabilise CO2 and limit temperature rise over the next century will be underestimated.

Eddy-driven low-frequency variability: physics and observability through altimetry

NASA Astrophysics Data System (ADS)

Penduff, Thierry; Sérazin, Guillaume; Arbic, Brian; Mueller, Malte; Richman, James G.; Shriver, Jay F.; Morten, Andrew J.; Scott, Robert B.

2015-04-01

Model studies have revealed the propensity of the eddying ocean circulation to generate strong low-frequency variability (LFV) intrinsically, i.e. without low-frequency atmospheric variability. In the present study, gridded satellite altimeter products, idealized quasi-geostrophic (QG) turbulent simulations, and realistic high-resolution global ocean simulations are used to study the spontaneous tendency of mesoscale (relatively high frequency and high wavenumber) kinetic energy to non-linearly cascade towards larger time and space scales. The QG model reveals that large-scale variability, arising from the well-known spatial inverse cascade, is associated with low frequencies. Low-frequency, low-wavenumber energy is maintained primarily by nonlinearities in the QG model, with forcing (by large-scale shear) and friction playing secondary roles. In realistic simulations, nonlinearities also generally drive kinetic energy to low frequencies and low wavenumbers. In some, but not all, regions of the gridded altimeter product, surface kinetic energy is also found to cascade toward low frequencies. Exercises conducted with the realistic model suggest that the spatial and temporal filtering inherent in the construction of gridded satellite altimeter maps may contribute to the discrepancies seen in some regions between the direction of frequency cascade in models versus gridded altimeter maps. Finally, the range of frequencies that are highly energized and engaged these cascades appears much greater than the range of highly energized and engaged wavenumbers. Global eddying simulations, performed in the context of the CHAOCEAN project in collaboration with the CAREER project, provide estimates of the range of timescales that these oceanic nonlinearities are likely to feed without external variability.

Modelling of a Convecting, Crystallizing, and Replenished Diopside-Anorthite Axial Magma Chamber beneath Mid Ocean Ridges

NASA Astrophysics Data System (ADS)

Lowell, R. P.; Lata, C.

2016-12-01

The aim of this work is to model heat output from a cooling, convective, crystallizing, and replenished basaltic magma sill, representing an axial magma lens (AML) at mid oceanic ridges. As a simplified version of basaltic melt, we have assumed the melt to be a two-component eutectic system composed of diopside and anorthite. Convective vigor is expressed through the Rayleigh number and heat flux is scaled through a classical relationship between the Rayleigh number and Nusselt number, where the temperature difference driving the convective heat flux is derived from a "viscous" temperature scale reflecting the strong temperature dependent viscosity of the system. Viscosity is modeled as a function of melt composition and temperature using the Tammann-Vogel-Fulcher equation, with parameters fit to the values of observed viscosities along the diopside-anorthite liquidus. It was observed for the un-replenished case, in which crystals fall rapidly to the floor of the AML, model results show that the higher initial concentration of diopside, the more vigorous the convection and the faster the rate of crystallization and decay of heat output. Replenishment of the AML accompanied by modest thickening of the melt layer stabilizes the heat output at values similar to those observed at ridge-axis hydrothermal systems. This study is an important step forward in quantitative understanding of thermal evolution of the axial magma lens at a mid-ocean ridge and the corresponding effect on high-temperature hydrothermal systems. Future work could involve improved replenishment mechanisms, more complex melts, and direct coupling with hydrothermal circulation models.

Interannual Variability of Tropical Ocean Evaporation: A Comparison of Microwave Satellite and Assimilation Results

NASA Technical Reports Server (NTRS)

Robertson, Franklin R.; Wick, Gary; Bosilovich, Michael G.

2005-01-01

Remote sensing methodologies for turbulent heat fluxes over oceans depend on driving bulk formulations of fluxes with measured surface winds and estimated near surface thermodynamics from microwave sensors of the Special Sensor Microwave Imager (SSM/I) heritage. We will review recent work with a number of SSM/I-based algorithms and investigate the ability of current data sets to document global, tropical ocean-averaged evaporation changes in association with El Nino and La Nina SST changes. We show that in addition to interannual signals, latent heat flux increases over the period since late 1987 range from approx. .1 to .6 mm/ day are present; these represent trends 2 to 3 times larger than the NCEP Reanalysis. Since atmospheric storage cannot account for the difference, and since compensating evapotranspiration changes over land are highly unlikely to be this large, these evaporation estimates cannot be reconciled with ocean precipitation records such as those produced by the Global Precipitation Climatology Project, GPCP. The reasons for the disagreement include less than adequate intercalibration between SSM/I sensors providing winds and water vapor for driving the algorithms, biases due to the assumption that column integrated water vapor mirrors near surface water vapor variations, and other factors as well. The reanalyses have their own problems with spin-up during assimilation, lack of constraining input data at the ocean surface, and amplitude of synoptic transients.

Integrated stratigraphy of the Cenomanian-Turonian boundary interval: improving understanding of Oceanic Anoxic Events

NASA Astrophysics Data System (ADS)

Jarvis, Ian

2014-05-01

The Cenomanian-Turonian boundary (CTB) interval ~ 94 Ma represented a period of major global palaeoenvironmental change. Increasingly detailed multidisciplinary studies integrating sedimentological, palaeontological and geochemical data from multiple basins, are enabling the development of refined but complex models that aid understanding of the mechanisms driving changes in ocean productivity and climate. This paper reviews some of the exciting new developments in this field. Facies change characterizes the CTB interval in most areas. In the Chalk seas of northern Europe, a widespead hiatus was followed by the deposition of clay-rich organic-lean beds of the Plenus Marl and its equivalents, and then nodular chalks. In the North Sea basin and its onshore extension in eastern England and northern Germany, black shales of the Black Band (Blodøks Formation, Hasseltal Formation) occur. Similarly, in northern Tethys, a brief interval of black shale accumulation within a predominantly carbonate succession, is exemplified by the Niveau Thomel in the Vocontian Basin (SE France), and the Livello Bonarelli in Italy. Widespread deposition of organic-rich marine sediments during CTB times led to 12C depletion in surface carbon reservoirs (oceans, atmosphere, biosphere), and a large positive global δ13C excursion preserved in marine carbonates and both marine and terrestrial organic matter (Oceanic Anoxic Event 2). Significant biotic turnover characterises the boundary interval, and inter-regional correlation may be achieved at high resolution using integrated biostratigraphy employing macrofossils (ammonites, inoceramid bivalves), microfossils (planktonic foraminifera, dinoflagellate cysts) and calcareous nannofossils. Correlations can be tested against those based on comparison of δ13C profiles - carbon isotope chemostratigraphy, supplemented by oxygen isotope and elemental data. Interpretation of paired carbonate - organic matter δ13C data from multiple CTB sections implicates rising atmospheric pCO2 linked to volcanic outgassing as a major forcing mechanism for palaeoclimate warming and palaeoceanographic change accompanying OAE2. New marine 187Os/188Os isotope stratigraphy further reveals the interaction of volcanism and ocean circulation during OAE2, and provides a further chemostratigraphic tool. Li isotope (δ 7Li) data may be interpreted as evidence that increased silicate weathering promoted by rising pCO2 acted as both a forcing and negative feedback mechanism driving OAE2 history. Neodymium and sulphur isotopes offer further insights into interactions between global biogeochemical cycles and ocean circulation changes.

Future change in ocean productivity: Is the Arctic the new Atlantic?

NASA Astrophysics Data System (ADS)

Yool, A.; Popova, E. E.; Coward, A. C.

2015-12-01

One of the most characteristic features in ocean productivity is the North Atlantic spring bloom. Responding to seasonal increases in irradiance and stratification, surface phytopopulations rise significantly, a pattern that visibly tracks poleward into summer. While blooms also occur in the Arctic Ocean, they are constrained by the sea-ice and strong vertical stratification that characterize this region. However, Arctic sea-ice is currently declining, and forecasts suggest this may lead to completely ice-free summers by the mid-21st century. Such change may open the Arctic up to Atlantic-style spring blooms, and do so at the same time as Atlantic productivity is threatened by climate change-driven ocean stratification. Here we use low and high-resolution instances of a coupled ocean-biogeochemistry model, NEMO-MEDUSA, to investigate productivity. Drivers of present-day patterns are identified, and changes in these across a climate change scenario (IPCC RCP 8.5) are analyzed. We find a globally significant decline in North Atlantic productivity (> -20%) by 2100, and a correspondingly significant rise in the Arctic (> +50%). However, rather than the future Arctic coming to resemble the current Atlantic, both regions are instead transitioning to a common, low nutrient regime. The North Pacific provides a counterexample where nutrients remain high and productivity increases with elevated temperature. These responses to climate change in the Atlantic and Arctic are common between model resolutions, suggesting an independence from resolution for key impacts. However, some responses, such as those in the North Pacific, differ between the simulations, suggesting the reverse and supporting the drive to more fine-scale resolutions. This article was corrected on 5 JAN 2016. See the end of the full text for details.

Evolution of Subducted Oceanic Crust in Dynamic Mantle Models

NASA Astrophysics Data System (ADS)

Brandenburg, J.; van Keken, P. E.; Ballentine, C.; Hauri, E.

2006-12-01

Isotopic ratios measured in oceanic basalts indicate the persistence of a highly differentiated and ancient mantle component. The provenance and distribution of this component are the subject of much discussion. A number of geodynamic studies have focused on the preservation of a chemically dense layer in the deepest mantle, while a smaller set of studies have explored the possibilities for its generation. We present an evaluation of the hypothesis that such a layer may represent the accumulation of subducted oceanic crust, with critical examination of the role that plate tectonics plays in mantle differentiation. In geodynamic models the treatment of plate tectonics controls crust production, subduction, and modulates the remixing rate. We use two methods for approximating plates in our models; prescription of a velocity boundary condition, and the force-balance method [1]. Emphasis is placed on the force-balance method, in which a numerical solution for the conservation of momentum is constructed by superposition. The force balance method has a minimum of free parameters compared to complex rheological descriptions that yield plate like behavior, and does not have the potential to artificially drive or hinder convection introduced by prescribing velocity boundary conditions. The mixing properties of the various methods are examined by comparison of embedded geochemical models for the isotopic evolution of Pb,U,Sm,Nd,Re,Os, and the noble gases. We find that the incorporation of strong plates leads to a mantle with increased stratification of heterogeneity. Sequestration of old oceanic crust in dense pools in the lowermost mantle is observed. However, the size and longevity of these dense pools decline considerably as realistic convective vigor is approached. Parameter space analysis is used to quantify this variability within the selection of models that reproduce Earth-like heat flow and plate velocities, and for comparison with the work of other authors. The residence time of old crust in pools and other areas of the mantle is examined with respect to the constraints imposed by isotope ratios observed in oceanic basalts. [1] Gable, C.W., R.J. O'Connell, B.J. Travis (1991) "Convection in 3 dimensions with surface plates; generation of a toroidal flow," J. Geophys. Res., 89, 8391--8405

Modeling shortwave radiative fluxes from satellites

NASA Astrophysics Data System (ADS)

Ma, Y.; Pinker, R. T.

2012-12-01

During the last two decades, significant progress has been made in assessing the Earth Radiation Balance from satellite observations. Yet, satellite based estimates differ from each other and from those provided by numerical models. Major issues are related to quality of satellite observations, such as the frequent changes in satellite observing systems, degradation of sensors, restricted spectral intervals and viewing geometry of sensors, and changes in the quality of atmospheric inputs that drive the inference schemes. To reduce differences among the satellite based estimates requires, among others, updates to inference schemes so that most recent auxiliary information can be fully utilized. This paper reports on improvements introduced to a methodology developed at the University of Maryland to estimate shortwave (SW) radiative fluxes within the atmosphere system from satellite observations, the implementation of the approach with newly available auxiliary information, evaluation of the downwelling SW flux against ground observations, and comparison with independent satellite methods and numerical models. Specifically, introduced are: new Narrow to Broadband (N/B) transformations and new Angular Distribution Models (ADM) for clear and cloudy sky that incorporate most recent land use classifications; improved aerosol treatment; separation of clouds by phase; improved sun-earth geometry; and implementation at 0.5° spatial resolution at 3-hourly intervals integrated to daily and monthly time scales. When compared to an earlier version of the model as implemented at 2.5° at global scale and against observations from the globally distributed Baseline Surface Radiation Network (BSRN) stations for a period of six years (at monthly time scale), the bias was reduced from 8.6 (4.6%) to -0.5 (0.3%) W/m2, the standard deviation from 16.6 (8.9%) to 14.5 (7.8%) W/m2while the correlation remained high at 0.98 in both cases. Evaluation was also done over oceanic sites as available from the Pilot Research Moored Array in the Tropical Atlantic (PIRATA) moorings and from the Tropical Atmosphere Ocean/Triangle Trans-Ocean Buoy Network (TAO/TRITON) moorings in the tropical Pacific Ocean. Overall, results over oceans were not as good as over land for all the satellite retrievals compared in this study.

A Crystallization-Temperature Profile Through Paleo-Oceanic Crust (Wadi Gideah Transect, Oman Ophiolite): Application of the REE-in-Plagioclase-Clinopyroxene Partitioning Thermometer

NASA Astrophysics Data System (ADS)

Mueller, S.; Hasenclever, J.; Garbe-Schönberg, D.; Koepke, J.; Hoernle, K.

2017-12-01

The accretion mechanisms forming oceanic crust at fast spreading ridges are still under controversial discussion. Thermal, petrological, and geochemical observations predict different end-member models, i.e., the gabbro glacier and the sheeted sill model. They all bear implications for heat transport, temperature distribution, mode of crystallization and hydrothermal heat removal over crustal depth. In a typical MOR setting, temperature is the key factor driving partitioning of incompatible elements during crystallization. LA-ICP-MS data for co-genetic plagioclase and clinopyroxene in gabbros along a transect through the plutonic section of paleo-oceanic crust (Wadi Gideah Transect, Oman ophiolite) reveal that REE partitioning coefficients are relatively constant in the layered gabbro section but increase for the overlying foliated gabbros, with an enhanced offset towards HREEs. Along with a systematic enrichment of REE's with crustal height, these trends are consistent with a system dominated by in-situ crystallization for the lower gabbros and a change in crystallization mode for the upper gabbros. Sun and Liang (2017) used experimental REE partitioning data for calibrating a new REE-in-plagioclase-clinopyroxene thermometer that we used here for establishing the first crystallization-temperature depth profile through oceanic crust that facilitates a direct comparison with thermal models of crustal accretion. Our results indicate crystallization temperatures of about 1220±8°C for the layered gabbros and lower temperatures of 1175±8°C for the foliated gabbros and a thermal minimum above the layered-to-foliated gabbro transition. Our findings are consistent with a hybrid accretion model for the oceanic crust. The thermal minimum is assumed to represent a zone where the descending crystal mushes originating from the axial melt lens meet with mushes that have crystallized in situ. These results can be used to verify and test thermal models (e.g., Maclennan et al., 2004, Theissen-Krah et al., 2016) and their predictions for heat flow and temperature distribution in the crust. Maclennan, J., Hulme, T., & Singh, S. C. (2004), G3, 5(2). / Sun, C., & Liang, Y., (2017), CMP, 172(4). / Theissen-Krah, S., Rüpke, L. H., & Hasenclever, J. (2016), GRL, 43(3).

Impact of air-sea drag coefficient for latent heat flux on large scale climate in coupled and atmosphere stand-alone simulations

NASA Astrophysics Data System (ADS)

Torres, Olivier; Braconnot, Pascale; Marti, Olivier; Gential, Luc

2018-05-01

The turbulent fluxes across the ocean/atmosphere interface represent one of the principal driving forces of the global atmospheric and oceanic circulation. Despite decades of effort and improvements, representation of these fluxes still presents a challenge due to the small-scale acting turbulent processes compared to the resolved scales of the models. Beyond this subgrid parameterization issue, a comprehensive understanding of the impact of air-sea interactions on the climate system is still lacking. In this paper we investigates the large-scale impacts of the transfer coefficient used to compute turbulent heat fluxes with the IPSL-CM4 climate model in which the surface bulk formula is modified. Analyzing both atmosphere and coupled ocean-atmosphere general circulation model (AGCM, OAGCM) simulations allows us to study the direct effect and the mechanisms of adjustment to this modification. We focus on the representation of latent heat flux in the tropics. We show that the heat transfer coefficients are highly similar for a given parameterization between AGCM and OAGCM simulations. Although the same areas are impacted in both kind of simulations, the differences in surface heat fluxes are substantial. A regional modification of heat transfer coefficient has more impact than uniform modification in AGCM simulations while in OAGCM simulations, the opposite is observed. By studying the global energetics and the atmospheric circulation response to the modification, we highlight the role of the ocean in dampening a large part of the disturbance. Modification of the heat exchange coefficient modifies the way the coupled system works due to the link between atmospheric circulation and SST, and the different feedbacks between ocean and atmosphere. The adjustment that takes place implies a balance of net incoming solar radiation that is the same in all simulations. As there is no change in model physics other than drag coefficient, we obtain similar latent heat flux between coupled simulations with different atmospheric circulations. Finally, we analyze the impact of model tuning and show that it can offset part of the feedbacks.

Making sense of ocean biota: how evolution and biodiversity of land organisms differ from that of the plankton.

PubMed

Smetacek, Victor

2012-09-01

The oceans cover 70% of the planet's surface, and their planktonic inhabitants generate about half the global primary production, thereby playing a key role in modulating planetary climate via the carbon cycle. The ocean biota have been under scientific scrutiny for well over a century, and yet our understanding of the processes driving natural selection in the pelagic environment - the open water inhabited by drifting plankton and free-swimming nekton - is still quite vague. Because of the fundamental differences in the physical environment, pelagic ecosystems function differently from the familiar terrestrial ecosystems of which we are a part. Natural selection creates biodiversity but understanding how this quality control of random mutations operates in the oceans - which traits are selected for under what circumstances and by which environmental factors, whether bottom-up or top-down - is currently a major challenge. Rapid advances in genomics are providing information, particularly in the prokaryotic realm, pertaining not only to the biodiversity inventory but also functional groups. This essay is dedicated to the poorly understood tribes of planktonic protists (unicellular eukaryotes) that feed the ocean's animals and continue to run the elemental cycles of our planet. It is an attempt at developing a conceptually coherent framework to understand the course of evolution by natural selection in the plankton and contrast it with the better-known terrestrial realm. I argue that organism interactions, in particular co-evolution between predators and prey (the arms race), play a central role in driving evolution in the pelagic realm. Understanding the evolutionary forces shaping ocean biota is a prerequisite for harnessing plankton for human purposes and also for protecting the oceanic ecosystems currently under severe stress from anthropogenic pressures.

Revealing and analyzing networks of environmental systems

NASA Astrophysics Data System (ADS)

Eveillard, D.; Bittner, L.; Chaffron, S.; Guidi, L.; Raes, J.; Karsenti, E.; Bowler, C.; Gorsky, G.

2015-12-01

Understanding the interactions between microbial communities and their environment well enough to be able to predict diversity on the basis of physicochemical parameters is a fundamental pursuit of microbial ecology that still eludes us. However, modeling microbial communities is a complicated task, because (i) communities are complex, (ii) most are described qualitatively, and (iii) quantitative understanding of the way communities interacts with their surroundings remains incomplete. Within this seminar, we will illustrate two complementary approaches that aim to overcome these points in different manners. First, we will present a network analysis that focus on the biological carbon pump in the global ocean. The biological carbon pump is the process by which photosynthesis transforms CO2 to organic carbon sinking to the deep-ocean as particles where it is sequestered. While the intensity of the pump correlate to plankton community composition, the underlying ecosystem structure and interactions driving this process remain largely uncharacterized Here we use environmental and metagenomic data gathered during the Tara Oceans expedition to improve understanding of these drivers. We show that specific plankton communities correlate with carbon export and highlight unexpected and overlooked taxa such as Radiolaria, alveolate parasites and bacterial pathogens, as well as Synechococcus and their phages, as key players in the biological pump. Additionally, we show that the abundances of just a few bacterial and viral genes predict most of the global ocean carbon export's variability. Together these findings help elucidate ecosystem drivers of the biological carbon pump and present a case study for scaling from genes-to-ecosystems. Second, we will show preliminary results on a probabilistic modeling that predicts microbial community structure across observed physicochemical data, from a putative network and partial quantitative knowledge. This modeling shows that, despite distinct quantitative environmental perturbations, the constraints on community structure could remain stable.

Robust global ocean cooling trend for the pre-industrial Common Era

NASA Astrophysics Data System (ADS)

McGregor, Helen V.; Evans, Michael N.; Goosse, Hugues; Leduc, Guillaume; Martrat, Belen; Addison, Jason A.; Mortyn, P. Graham; Oppo, Delia W.; Seidenkrantz, Marit-Solveig; Sicre, Marie-Alexandrine; Phipps, Steven J.; Selvaraj, Kandasamy; Thirumalai, Kaustubh; Filipsson, Helena L.; Ersek, Vasile

2015-09-01

The oceans mediate the response of global climate to natural and anthropogenic forcings. Yet for the past 2,000 years -- a key interval for understanding the present and future climate response to these forcings -- global sea surface temperature changes and the underlying driving mechanisms are poorly constrained. Here we present a global synthesis of sea surface temperatures for the Common Era (CE) derived from 57 individual marine reconstructions that meet strict quality control criteria. We observe a cooling trend from 1 to 1800 CE that is robust against explicit tests for potential biases in the reconstructions. Between 801 and 1800 CE, the surface cooling trend is qualitatively consistent with an independent synthesis of terrestrial temperature reconstructions, and with a sea surface temperature composite derived from an ensemble of climate model simulations using best estimates of past external radiative forcings. Climate simulations using single and cumulative forcings suggest that the ocean surface cooling trend from 801 to 1800 CE is not primarily a response to orbital forcing but arises from a high frequency of explosive volcanism. Our results show that repeated clusters of volcanic eruptions can induce a net negative radiative forcing that results in a centennial and global scale cooling trend via a decline in mixed-layer oceanic heat content.

Robust global ocean cooling trend for the pre-industrial Common Era

USGS Publications Warehouse

McGregor, Helen V.; Evans, Michael N.; Goosse, Hugues; Leduc, Guillaume; Martrat, Belen; Addison, Jason A.; Mortyn, P. Graham; Oppo, Delia W.; Seidenkrantz, Marit-Solveig; Sicre, Marie-Alexandrine; Phipps, Steven J.; Selvaraj, Kandasamy; Thirumalai, Kaustubh; Filipsson, Helena L.; Ersek, Vasile

2015-01-01

The oceans mediate the response of global climate to natural and anthropogenic forcings. Yet for the past 2,000 years — a key interval for understanding the present and future climate response to these forcings — global sea surface temperature changes and the underlying driving mechanisms are poorly constrained. Here we present a global synthesis of sea surface temperatures for the Common Era (CE) derived from 57 individual marine reconstructions that meet strict quality control criteria. We observe a cooling trend from 1 to 1800 CEthat is robust against explicit tests for potential biases in the reconstructions. Between 801 and 1800 CE, the surface cooling trend is qualitatively consistent with an independent synthesis of terrestrial temperature reconstructions, and with a sea surface temperature composite derived from an ensemble of climate model simulations using best estimates of past external radiative forcings. Climate simulations using single and cumulative forcings suggest that the ocean surface cooling trend from 801 to 1800 CE is not primarily a response to orbital forcing but arises from a high frequency of explosive volcanism. Our results show that repeated clusters of volcanic eruptions can induce a net negative radiative forcing that results in a centennial and global scale cooling trend via a decline in mixed-layer oceanic heat content.

Impact of ice-shelf sediment content on the dynamics of plumes under melting ice shelves

NASA Astrophysics Data System (ADS)

Wells, A.

2015-12-01

When a floating ice shelf melts into an underlying warm salty ocean, the resulting fresh meltwater can rise in a buoyant Ice-Shelf-Water plume under the ice. In certain settings, ice flowing across the grounding line carries a basal layer of debris rich ice, entrained via basal freezing around till in the upstream ice sheet. Melting of this debris-laden ice from floating ice shelves provides a flux of dense sediment to the ocean, in addition to the release of fresh buoyant meltwater. This presentation considers the impact of the resulting suspended sediment on the dynamics of ice shelf water plumes, and identifies two key flow regimes depending on the sediment concentration frozen into the basal ice layer. For large sediment concentration, melting of the debris-laden ice shelf generates dense convectively unstable waters that drive convective overturning into the underlying ocean. For lower sediment concentration, the sediment initially remains suspended in a buoyant meltwater plume rising along the underside of the ice shelf, before slowly depositing into the underlying ocean. A theoretical plume model is used to evaluate the significance of the negatively buoyant sediment on circulation strength and the feedbacks on melting rate, along with the expected depositional patterns under the ice shelf.

Three modes of interdecadal trends in sea surface temperature and sea surface height

NASA Astrophysics Data System (ADS)

Gnanadesikan, A.; Pradal, M.

2013-12-01

It might be thought that sea surface height and sea surface temperature would be tightly related. We show that this is not necessarily the case on a global scale. We analysed this relationship in a suite of coupled climate models run under 1860 forcing conditions. The models are low-resolution variants of the GFDL Earth System Model, reported in Galbraith et al. (J. Clim. 2011). 1. Correlated changes in global sea surface height and global sea surface temperature. This mode corresponds to opening and closing of convective chimneys in the Southern Ocean. As the Southern Ocean destratifies, sea ice formation is suppressed during the winter and more heat is taken up during the summer. This mode of variability is highly correlated with changes in the top of the atmosphere radiative budget and weakly correlated with changes in the deep ocean circulation. 2. Uncorrelated changes in global sea surface height and global sea surface temperature. This mode of variability is associated with interdecadal variabliity in tropical winds. Changes in the advective flux of heat to the surface ocean play a critical role in driving these changes, which also result in significant local changes in sea level. Changes sea ice over the Southern Ocean still result in changes in solar absorption, but these are now largely cancelled by changes in outgoing longwave radiation. 3. Anticorrelated changes in global sea surface height and global sea surface temperatures. By varying the lateral diffusion coefficient in the ocean model, we are able to enhance and suppress convection in the Southern and Northern Pacific Oceans. Increasing the lateral diffusion coefficients shifts the balance sources of deep water away from the warm salty deep water of the North Atlantic and towards cold fresh deep water from the other two regions. As a result, even though the planet as a whole warms, the deep ocean cools and sea level falls, with changes of order 30 cm over 500 years. The increase in solar absorption in polar regions is more than compensated by an increase in outgoing longwave radiation. Relationship between global SSH trend over a decade and (A) local SSH change over a decade (m/m). (B) Global SST change over a decade (m/K) (C) Portion of decadal SST change correlated with net radiation at the top of the atmosphere (m/K) (D) Portion of decadal SST change not correlated with net radiation at the top of the atmosphere.

A numerical model investigation of the impacts of Hurricane Sandy on water level variability in Great South Bay, New York

USGS Publications Warehouse

Bennett, Vanessa C. C.; Mulligan, Ryan P.; Hapke, Cheryl J.

2018-01-01

Hurricane Sandy was a large and intense storm with high winds that caused total water levels from combined tides and storm surge to reach 4.0 m in the Atlantic Ocean and 2.5 m in Great South Bay (GSB), a back-barrier bay between Fire Island and Long Island, New York. In this study the impact of the hurricane winds and waves are examined in order to understand the flow of ocean water into the back-barrier bay and water level variations within the bay. To accomplish this goal, a high resolution hurricane wind field is used to drive the coupled Delft3D-SWAN hydrodynamic and wave models over a series of grids with the finest resolution in GSB. The processes that control water levels in the back-barrier bay are investigated by comparing the results of four cases that include: (i) tides only; (ii) tides, winds and waves with no overwash over Fire Island allowed; (iii) tides, winds, waves and limited overwash at the east end of the island; (iv) tides, winds, waves and extensive overwash along the island. The results indicate that strong local wind-driven storm surge along the bay axis had the largest influence on the total water level fluctuations during the hurricane. However, the simulations allowing for overwash have higher correlation with water level observations in GSB and suggest that island overwash provided a significant contribution of ocean water to eastern GSB during the storm. The computations indicate that overwash of 7500–10,000 m3s−1 was approximately the same as the inflow from the ocean through the major existing inlet. Overall, the model results indicate the complex variability in total water levels driven by tides, ocean storm surge, surge from local winds, and overwash that had a significant impact on the circulation in Great South Bay during Hurricane Sandy.

South Atlantic meridional transports from NEMO-based simulations and reanalyses

NASA Astrophysics Data System (ADS)

Mignac, Davi; Ferreira, David; Haines, Keith

2018-02-01

The meridional heat transport (MHT) of the South Atlantic plays a key role in the global heat budget: it is the only equatorward basin-scale ocean heat transport and it sets the northward direction of the global cross-equatorial transport. Its strength and variability, however, are not well known. The South Atlantic transports are evaluated for four state-of-the-art global ocean reanalyses (ORAs) and two free-running models (FRMs) in the period 1997-2010. All products employ the Nucleus for European Modelling of the Oceans (NEMO) model, and the ORAs share very similar configurations. Very few previous works have looked at ocean circulation patterns in reanalysis products, but here we show that the ORA basin interior transports are consistently improved by the assimilated in situ and satellite observations relative to the FRMs, especially in the Argo period. The ORAs also exhibit systematically higher meridional transports than the FRMs, which is in closer agreement with observational estimates at 35 and 11° S. However, the data assimilation impact on the meridional transports still greatly varies among the ORAs, leading to differences up to ˜ 8 Sv and 0.4 PW in the South Atlantic Meridional Overturning Circulation and the MHTs, respectively. We narrow this down to large inter-product discrepancies in the western boundary currents (WBCs) at both upper and deep levels explaining up to ˜ 85 % of the inter-product differences in MHT. We show that meridional velocity differences, rather than temperature differences, in the WBCs drive ˜ 83 % of this MHT spread. These findings show that the present ocean observation network and data assimilation schemes can be used to consistently constrain the South Atlantic interior circulation but not the overturning component, which is dominated by the narrow western boundary currents. This will likely limit the effectiveness of ORA products for climate or decadal prediction studies.

A numerical model investigation of the impacts of Hurricane Sandy on water level variability in Great South Bay, New York

NASA Astrophysics Data System (ADS)

Bennett, Vanessa C. C.; Mulligan, Ryan P.; Hapke, Cheryl J.

2018-06-01

Hurricane Sandy was a large and intense storm with high winds that caused total water levels from combined tides and storm surge to reach 4.0 m in the Atlantic Ocean and 2.5 m in Great South Bay (GSB), a back-barrier bay between Fire Island and Long Island, New York. In this study the impact of the hurricane winds and waves are examined in order to understand the flow of ocean water into the back-barrier bay and water level variations within the bay. To accomplish this goal, a high resolution hurricane wind field is used to drive the coupled Delft3D-SWAN hydrodynamic and wave models over a series of grids with the finest resolution in GSB. The processes that control water levels in the back-barrier bay are investigated by comparing the results of four cases that include: (i) tides only; (ii) tides, winds and waves with no overwash over Fire Island allowed; (iii) tides, winds, waves and limited overwash at the east end of the island; (iv) tides, winds, waves and extensive overwash along the island. The results indicate that strong local wind-driven storm surge along the bay axis had the largest influence on the total water level fluctuations during the hurricane. However, the simulations allowing for overwash have higher correlation with water level observations in GSB and suggest that island overwash provided a significant contribution of ocean water to eastern GSB during the storm. The computations indicate that overwash of 7500-10,000 m3s-1 was approximately the same as the inflow from the ocean through the major existing inlet. Overall, the model results indicate the complex variability in total water levels driven by tides, ocean storm surge, surge from local winds, and overwash that had a significant impact on the circulation in Great South Bay during Hurricane Sandy.

Sensitivity of ocean model simulation in the coastal ocean to the resolution of the meteorological forcing

NASA Astrophysics Data System (ADS)

Chen, Feng; Shapiro, Georgy; Thain, Richard

2013-04-01

The quality of ocean simulations depends on a number of factors such as approximations in governing equations, errors introduced by the numerical scheme, uncertainties in input parameters, and atmospheric forcing. The identification of relations between the uncertainties in input and output data is still a challenge for the development of numerical models. The impacts of ocean variables on ocean models are still not well known (e.g., Kara et al., 2009). Given the considerable importance of the atmospheric forcing to the air-sea interaction, it is essential that researchers in ocean modelling work need a good understanding about how sensitive the atmospheric forcing is to variations of model results, which is beneficial to the development of ocean models. Also, it provides a proper way to choose the atmospheric forcing in ocean modelling applications. Our previous study (Shapiro et al, 2011) has shown that the basin-wide circulation pattern and the temperature structure in the Black Sea produced by the same model is significantly dependent on the source of the meteorological input, giving remarkably different responses. For the purpose of this study we have chosen the Celtic Sea where high resolution meteo data are available from the UK Met office since 2006. The Celtic Sea is tidally dominated water basin, with the tidal stream amplitude varying from 0.25m/s in the southwest to 2 m/s in the Bristol Channel. It is also filled with mesoscale eddies which contribute to the formation of the residual (tidally averaged) circulation pattern (Young et al, 2003). The sea is strongly stratified from April to November, which adds to the formation of density driven currents. In this paper we analyse how sensitive the model output is to variations in the spatial resolution of meteorological using low (1.6°) and high (0.11°) resolution meteo forcing, giving the quantitative relation between variations of met forcing and the resulted differences of model results, as well as identifying the causes. The length scales of most energetic dynamic features in both ocean and atmosphere are defined by the Rossby radius of deformation, which is about 1000 km (a typical size of a cyclone) in the atmosphere while only 10-20 km (a size of a mesoscale eddy) in a shallow sea. However sub-mesoscale atmospheric patterns such as patchiness in the cloud cover could result in smaller scale variations of both the wind and solar radiation hence creating a direct link of these smaller atmospheric features with the ocean mesoscale variability. The simulation has been performed using a version of POLCOMS numerical model (Enriquez et al, 2005). Tidal boundary conditions were taken from the Oregon State University European Shelf Tidal Model (Egbert et al, 2010) and the temperature/ salinity initial fields and boundary conditions were taken from the World Ocean Database (Boyer et al, 2004). The paper discusses what elements of the circulation and water column structure are mostly sensitive to the meteo-fields resolution. References Kara, A.B., Wallcraft, A.J., Hurlburt, H.E., Loh, W.-Y., 2009. Which surface atmospheric variable drives the seasonal cycle of sea surface temperature over the global ocean? Journal of Geophysical Research, Vol. 114, D05101. Boyer, .T, S. Levitus, H. Garcia, R. Locarnini, C. Stephens, and J. Antonov, T. Boyer, S. Levitus, H. Garcia, R. Locarnini, C. Stephens, and J. Antonov, 2004. Objective Analyses of Annual, Seasonal, and Monthly Temperature and Salinity for the World Ocean on a ¼ Grid. International Journal of Climatology, 25, 931-945. Egbert, G. D., S. Y. Erofeeva, and R. D. Ray, 2010. Assimilation of altimetry data for nonlinear shallow-water tides: quarter-diurnal tides of the Northwest European Shelf, Continental Shelf Research, 30, 668-679. Enriquez, C. E., G. I. Shapiro, A. J. Souza, and A. G. Zatsepin, 2005. Hydrodynamic modelling of mesoscale eddies in the Black Sea. Ocean Dyn., 55, 476-489. Georgy Shapiro, Dmitry Aleynik , Andrei Zatsepin , Valentina Khan, Valery Prostakishin , Tatiana Akivis , Vladimir Belokopytov , Anton Sviridov , and Vladimir Piotukh . 2011. Response of water temperature in the Black Sea to atmospheric forcing: the sensitivity study. Geophysical Research Abstracts. Vol. 13, EGU2011-933

Fit to predict? Eco-informatics for predicting the catchability of a pelagic fish in near real time.

PubMed

Scales, Kylie L; Hazen, Elliott L; Maxwell, Sara M; Dewar, Heidi; Kohin, Suzanne; Jacox, Michael G; Edwards, Christopher A; Briscoe, Dana K; Crowder, Larry B; Lewison, Rebecca L; Bograd, Steven J

2017-12-01

The ocean is a dynamic environment inhabited by a diverse array of highly migratory species, many of which are under direct exploitation in targeted fisheries. The timescales of variability in the marine realm coupled with the extreme mobility of ocean-wandering species such as tuna and billfish complicates fisheries management. Developing eco-informatics solutions that allow for near real-time prediction of the distributions of highly mobile marine species is an important step towards the maturation of dynamic ocean management and ecological forecasting. Using 25 yr (1990-2014) of NOAA fisheries' observer data from the California drift gillnet fishery, we model relative probability of occurrence (presence-absence) and catchability (total catch per gillnet set) of broadbill swordfish Xiphias gladius in the California Current System. Using freely available environmental data sets and open source software, we explore the physical drivers of regional swordfish distribution. Comparing models built upon remotely sensed data sets with those built upon a data-assimilative configuration of the Regional Ocean Modelling System (ROMS), we explore trade-offs in model construction, and address how physical data can affect predictive performance and operational capacity. Swordfish catchability was found to be highest in deeper waters (>1,500 m) with surface temperatures in the 14-20°C range, isothermal layer depth (ILD) of 20-40 m, positive sea surface height (SSH) anomalies, and during the new moon (<20% lunar illumination). We observed a greater influence of mesoscale variability (SSH, wind speed, isothermal layer depth, eddy kinetic energy) in driving swordfish catchability (total catch) than was evident in predicting the relative probability of presence (presence-absence), confirming the utility of generating spatiotemporally dynamic predictions. Data-assimilative ROMS circumvent the limitations of satellite remote sensing in providing physical data fields for species distribution models (e.g., cloud cover, variable resolution, subsurface data), and facilitate broad-scale prediction of dynamic species distributions in near real time. © 2017 by the Ecological Society of America.

Modeling the global emission, transport and deposition of trace elements associated with mineral dust

DOE PAGES

Zhang, Y.; Mahowald, N.; Scanza, R. A.; ...

2015-10-12

Trace element deposition from desert dust has important impacts on ocean primary productivity, the quantification of which could be useful in determining the magnitude and sign of the biogeochemical feedback on radiative forcing. However, the impact of elemental deposition to remote ocean regions is not well understood and is not currently included in global climate models. In this study, emission inventories for eight elements primarily of soil origin, Mg, P, Ca, Mn, Fe, K, Al, and Si are determined based on a global mineral data set and a soil data set. The resulting elemental fractions are used to drive themore » desert dust model in the Community Earth System Model (CESM) in order to simulate the elemental concentrations of atmospheric dust. Spatial variability of mineral dust elemental fractions is evident on a global scale, particularly for Ca. Simulations of global variations in the Ca / Al ratio, which typically range from around 0.1 to 5.0 in soils, are consistent with observations, suggesting that this ratio is a good signature for dust source regions. The simulated variable fractions of chemical elements are sufficiently different; estimates of deposition should include elemental variations, especially for Ca, Al and Fe. The model results have been evaluated with observations of elemental aerosol concentrations from desert regions and dust events in non-dust regions, providing insights into uncertainties in the modeling approach. The ratios between modeled and observed elemental fractions range from 0.7 to 1.6, except for Mg and Mn (3.4 and 3.5, respectively). Using the soil database improves the correspondence of the spatial heterogeneity in the modeling of several elements (Ca, Al and Fe) compared to observations. Total and soluble dust element fluxes to different ocean basins and ice sheet regions have been estimated, based on the model results. The annual inputs of soluble Mg, P, Ca, Mn, Fe and K associated with dust using the mineral data set are 0.30 Tg, 16.89 Gg, 1.32 Tg, 22.84 Gg, 0.068 Tg, and 0.15 Tg to global oceans and ice sheets.« less

Marine phytoplankton stoichiometry mediates nonlinear interactions between nutrient supply, temperature, and atmospheric CO2

NASA Astrophysics Data System (ADS)

Moreno, Allison R.; Hagstrom, George I.; Primeau, Francois W.; Levin, Simon A.; Martiny, Adam C.

2018-05-01

Marine phytoplankton stoichiometry links nutrient supply to marine carbon export. Deviations of phytoplankton stoichiometry from Redfield proportions (106C : 1P) could therefore have a significant impact on carbon cycling, and understanding which environmental factors drive these deviations may reveal new mechanisms regulating the carbon cycle. To explore the links between environmental conditions, stoichiometry, and carbon cycling, we compared four different models of phytoplankton C : P: a fixed Redfield model, a model with C : P given as a function of surface phosphorus concentration (P), a model with C P given as a function of temperature, and a new multi-environmental model that predicts C : P as a function of light, temperature, and P. These stoichiometric models were embedded into a five-box ocean circulation model, which resolves the three major ocean biomes (high-latitude, subtropical gyres, and tropical upwelling regions). Contrary to the expectation of a monotonic relationship between surface nutrient drawdown and carbon export, we found that lateral nutrient transport from lower C : P tropical waters to high C : P subtropical waters could cause carbon export to decrease with increased tropical nutrient utilization. It has been hypothesized that a positive feedback between temperature and pCO2, atm will play an important role in anthropogenic climate change, with changes in the biological pump playing at most a secondary role. Here we show that environmentally driven shifts in stoichiometry make the biological pump more influential, and may reverse the expected positive relationship between temperature and pCO2, atm. In the temperature-only model, changes in tropical temperature have more impact on the Δ pCO2, atm (˜ 41 ppm) compared to subtropical temperature changes (˜ 4.5 ppm). Our multi-environmental model predicted a decline in pCO2, atm of ˜ 46 ppm when temperature spanned a change of 10 °C. Thus, we find that variation in marine phytoplankton stoichiometry and its environmental controlling factors can lead to nonlinear controls on pCO2, atm, suggesting the need for further studies of ocean C : P and the impact on ocean carbon cycling.

Satellite observations and modeling of oil spill trajectories in the Bohai Sea.

PubMed

Xu, Qing; Li, Xiaofeng; Wei, Yongliang; Tang, Zeyan; Cheng, Yongcun; Pichel, William G

2013-06-15

On June 4 and 17, 2011, separate oil spill accidents occurred at two oil platforms in the Bohai Sea, China. The oil spills were subsequently observed on different types of satellite images including SAR (Synthetic Aperture Radar), Chinese HJ-1-B CCD and NASA MODIS. To illustrate the fate of the oil spills, we performed two numerical simulations to simulate the trajectories of the oil spills with the GNOME (General NOAA Operational Modeling Environment) model. For the first time, we drive the GNOME with currents obtained from an operational ocean model (NCOM, Navy Coastal Ocean Model) and surface winds from operational scatterometer measurements (ASCAT, the Advanced Scatterometer). Both data sets are freely and openly available. The initial oil spill location inputs to the model are based on the detected oil spill locations from the SAR images acquired on June 11 and 14. Three oil slicks are tracked simultaneously and our results show good agreement between model simulations and subsequent satellite observations in the semi-enclosed shallow sea. Moreover, GNOME simulation shows that the number of 'splots', which denotes the extent of spilled oil, is a vital factor for GNOME running stability when the number is less than 500. Therefore, oil spill area information obtained from satellite sensors, especially SAR, is an important factor for setting up the initial model conditions. Copyright © 2013 Elsevier Ltd. All rights reserved.

Impacts of ENSO on air-sea oxygen exchange: Observations and mechanisms

NASA Astrophysics Data System (ADS)

Eddebbar, Yassir A.; Long, Matthew C.; Resplandy, Laure; Rödenbeck, Christian; Rodgers, Keith B.; Manizza, Manfredi; Keeling, Ralph F.

2017-05-01

Models and observations of atmospheric potential oxygen (APO ≃ O2 + 1.1 * CO2) are used to investigate the influence of El Niño-Southern Oscillation (ENSO) on air-sea O2 exchange. An atmospheric transport inversion of APO data from the Scripps flask network shows significant interannual variability in tropical APO fluxes that is positively correlated with the Niño3.4 index, indicating anomalous ocean outgassing of APO during El Niño. Hindcast simulations of the Community Earth System Model (CESM) and the Institut Pierre-Simon Laplace model show similar APO sensitivity to ENSO, differing from the Geophysical Fluid Dynamics Laboratory model, which shows an opposite APO response. In all models, O2 accounts for most APO flux variations. Detailed analysis in CESM shows that the O2 response is driven primarily by ENSO modulation of the source and rate of equatorial upwelling, which moderates the intensity of O2 uptake due to vertical transport of low-O2 waters. These upwelling changes dominate over counteracting effects of biological productivity and thermally driven O2 exchange. During El Niño, shallower and weaker upwelling leads to anomalous O2 outgassing, whereas deeper and intensified upwelling during La Niña drives enhanced O2 uptake. This response is strongly localized along the central and eastern equatorial Pacific, leading to an equatorial zonal dipole in atmospheric anomalies of APO. This dipole is further intensified by ENSO-related changes in winds, reconciling apparently conflicting APO observations in the tropical Pacific. These findings suggest a substantial and complex response of the oceanic O2 cycle to climate variability that is significantly (>50%) underestimated in magnitude by ocean models.

Hourly changes in sea surface salinity in coastal waters recorded by Geostationary Ocean Color Imager

NASA Astrophysics Data System (ADS)

Liu, Rongjie; Zhang, Jie; Yao, Haiyan; Cui, Tingwei; Wang, Ning; Zhang, Yi; Wu, Lingjuan; An, Jubai

2017-09-01

In this study, we monitored hourly changes in sea surface salinity (SSS) in turbid coastal waters from geostationary satellite ocean color images for the first time, using the Bohai Sea as a case study. We developed a simple multi-linear statistical regression model to retrieve SSS data from Geostationary Ocean Color Imager (GOCI) based on an in situ satellite matched-up dataset (R2 = 0.795; N = 41; Range: 26.4 to 31.9 psμ). The model was then validated using independent continuous SSS measurements from buoys, with the average percentage difference of 0.65%. The model was applied to GOCI images from the dry season during an astronomical tide to characterize hourly changes in SSS in the Bohai Sea. We found that the model provided reasonable estimates of the hourly changes in SSS and that trends in the modeled and measured data were similar in magnitude and direction (0.43 vs 0.33 psμ, R2 = 0.51). There were clear diurnal variations in the SSS of the Bohai Sea, with a regional average of 0.455 ± 0.079 psμ (0.02-3.77 psμ). The magnitude of the diurnal variations in SSS varied spatially, with large diurnal variability in the nearshore, particularly in the estuary, and small variability in the offshore area. The model for the riverine area was based on the inverse correlation between SSS and CDOM absorption. In the offshore area, the water mass of the North Yellow Sea, characterized by high SSS and low CDOM concentrations, dominated. Analysis of the driving mechanisms showed that the tidal current was the main control on hourly changes in SSS in the Bohai Sea.

Assessment of Energy Production Potential from Ocean Currents along the United States Coastline

DOE Office of Scientific and Technical Information (OSTI.GOV)

Haas, Kevin

Increasing energy consumption and depleting reserves of fossil fuels have resulted in growing interest in alternative renewable energy from the ocean. Ocean currents are an alternative source of clean energy due to their inherent reliability, persistence and sustainability. General ocean circulations exist in the form of large rotating ocean gyres, and feature extremely rapid current flow in the western boundaries due to the Coriolis Effect. The Gulf Stream system is formed by the western boundary current of the North Atlantic Ocean that flows along the east coastline of the United States, and therefore is of particular interest as a potentialmore » energy resource for the United States. This project created a national database of ocean current energy resources to help advance awareness and market penetration in ocean current energy resource assessment. The database, consisting of joint velocity magnitude and direction probability histograms, was created from data created by seven years of numerical model simulations. The accuracy of the database was evaluated by ORNL?s independent validation effort documented in a separate report. Estimates of the total theoretical power resource contained in the ocean currents were calculated utilizing two separate approaches. Firstly, the theoretical energy balance in the Gulf Stream system was examined using the two-dimensional ocean circulation equations based on the assumptions of the Stommel model for subtropical gyres with the quasi-geostrophic balance between pressure gradient, Coriolis force, wind stress and friction driving the circulation. Parameters including water depth, natural dissipation rate and wind stress are calibrated in the model so that the model can reproduce reasonable flow properties including volume flux and energy flux. To represent flow dissipation due to turbines additional turbine drag coefficient is formulated and included in the model. Secondly, to determine the reasonableness of the total power estimates from the Stommel model and to help determine the size and capacity of arrays necessary to extract the maximum theoretical power, further estimates of the available power based on the distribution of the kinetic power density in the undisturbed flow was completed. This used estimates of the device spacing and scaling to sum up the total power that the devices would produce. The analysis has shown that considering extraction over a region comprised of the Florida Current portion of the Gulf Stream system, the average power dissipated ranges between 4-6 GW with a mean around 5.1 GW. This corresponds to an average of approximately 45 TWh/yr. However, if the extraction area comprises the entire portion of the Gulf Stream within 200 miles of the US coastline from Florida to North Carolina, the average power dissipated becomes 18.6 GW or 163 TWh/yr. A web based GIS interface, http://www.oceancurrentpower.gatech.edu/, was developed for dissemination of the data. The website includes GIS layers of monthly and yearly mean ocean current velocity and power density for ocean currents along the entire coastline of the United States, as well as joint and marginal probability histograms for current velocities at a horizontal resolution of 4-7 km with 10-25 bins over depth. Various tools are provided for viewing, identifying, filtering and downloading the data.« less

Microplastic distribution in global marine surface waters: results of an extensive citizen science study

NASA Astrophysics Data System (ADS)

Barrows, A.; Petersen, C.

2017-12-01

Plastic is a major pollutant throughout the world. The majority of the 322 million tons produced annually is used for single-use packaging. What makes plastic an attractive packaging material: cheap, light-weight and durable are also the features that help make it a common and persistent pollutant. There is a growing body of research on microplastic, particles less than 5 mm in size. Microfibers are the most common microplastic in the marine environment. Global estimates of marine microplastic surface concentrations are based on relatively small sample sizes when compared to the vast geographic scale of the ocean. Microplastic residence time and movement along the coast and sea surface outside of the gyres is still not well researched. This five-year project utilized global citizen scientists to collect 1,628 1-liter surface grab samples in every major ocean. The Artic and Southern oceans contained highest average of particles per liter of surface water. Open ocean samples (further than 12 nm from land, n = 686) contained a higher particle average (17 pieces L-1) than coastal samples (n = 723) 6 pieces L-1. Particles were predominantly 100 µm- 1.5 mm in length (77%), smaller than what has been captured in the majority of surface studies. Utilization of citizen scientists to collect data both in fairly accessible regions of the world as well as from areas hard to reach and therefore under sampled, provides us with a wider perspective of global microplastics occurrence. Our findings confirm global microplastic accumulation zone model predictions. The open ocean and poles have sequestered and trapped plastic for over half a century, and show that not only plastics, but anthropogenic fibers are polluting the environment. Continuing to fill knowledge gaps on microplastic shape, size and color in remote ocean areas will drive more accurate oceanographic models of plastic accumulation zones. Incorporation of smaller-sized particles in these models, which has previously been lacking, will help to better understand potential fate and transformation microplastic and anthropogenic particles in the marine environment.

Impact of anthropogenic atmospheric nitrogen and sulfur deposition on ocean acidification and the inorganic carbon system.

PubMed

Doney, Scott C; Mahowald, Natalie; Lima, Ivan; Feely, Richard A; Mackenzie, Fred T; Lamarque, Jean-Francois; Rasch, Phil J

2007-09-11

Fossil fuel combustion and agriculture result in atmospheric deposition of 0.8 Tmol/yr reactive sulfur and 2.7 Tmol/yr nitrogen to the coastal and open ocean near major source regions in North America, Europe, and South and East Asia. Atmospheric inputs of dissociation products of strong acids (HNO(3) and H2SO(4)) and bases (NH(3)) alter surface seawater alkalinity, pH, and inorganic carbon storage. We quantify the biogeochemical impacts by using atmosphere and ocean models. The direct acid/base flux to the ocean is predominately acidic (reducing total alkalinity) in the temperate Northern Hemisphere and alkaline in the tropics because of ammonia inputs. However, because most of the excess ammonia is nitrified to nitrate (NO(3)(-)) in the upper ocean, the effective net atmospheric input is acidic almost everywhere. The decrease in surface alkalinity drives a net air-sea efflux of CO(2), reducing surface dissolved inorganic carbon (DIC); the alkalinity and DIC changes mostly offset each other, and the decline in surface pH is small. Additional impacts arise from nitrogen fertilization, leading to elevated primary production and biological DIC drawdown that reverses in some places the sign of the surface pH and air-sea CO(2) flux perturbations. On a global scale, the alterations in surface water chemistry from anthropogenic nitrogen and sulfur deposition are a few percent of the acidification and DIC increases due to the oceanic uptake of anthropogenic CO(2). However, the impacts are more substantial in coastal waters, where the ecosystem responses to ocean acidification could have the most severe implications for mankind.

Ocean acidification affects coral growth by reducing skeletal density.

PubMed

Mollica, Nathaniel R; Guo, Weifu; Cohen, Anne L; Huang, Kuo-Fang; Foster, Gavin L; Donald, Hannah K; Solow, Andrew R

2018-02-20

Ocean acidification (OA) is considered an important threat to coral reef ecosystems, because it reduces the availability of carbonate ions that reef-building corals need to produce their skeletons. However, while theory predicts that coral calcification rates decline as carbonate ion concentrations decrease, this prediction is not consistently borne out in laboratory manipulation experiments or in studies of corals inhabiting naturally low-pH reefs today. The skeletal growth of corals consists of two distinct processes: extension (upward growth) and densification (lateral thickening). Here, we show that skeletal density is directly sensitive to changes in seawater carbonate ion concentration and thus, to OA, whereas extension is not. We present a numerical model of Porites skeletal growth that links skeletal density with the external seawater environment via its influence on the chemistry of coral calcifying fluid. We validate the model using existing coral skeletal datasets from six Porites species collected across five reef sites and use this framework to project the impact of 21st century OA on Porites skeletal density across the global tropics. Our model predicts that OA alone will drive up to 20.3 ± 5.4% decline in the skeletal density of reef-building Porites corals.

Effect of gravity waves on the North Atlantic circulation

NASA Astrophysics Data System (ADS)

Eden, Carsten

2017-04-01

The recently proposed IDEMIX (Internal wave Dissipation, Energy and MIXing) parameterisation for the effect of gravity waves offers the possibility to construct consistent ocean models with a closed energy cycle. This means that the energy available for interior mixing in the ocean is only controlled by external energy input from the atmosphere and the tidal system and by internal exchanges. A central difficulty is the unknown fate of meso-scale eddy energy. In different scenarios for that eddy dissipation, the parameterized internal wave field provides between 2 and 3 TW for interior mixing from the total external energy input of about 4 TW, such that a transfer between 0.3 and 0.4 TW into mean potential energy contributes to drive the large-scale circulation in the model. The impact of the different mixing on the meridional overturning in the North Atlantic is discussed and compared to hydrographic observations. Furthermore, the direct energy exchange of the wave field with the geostrophic flow is parameterized in extended IDEMIX versions and the sensitivity of the North Atlantic circulation by this gravity wave drag is discussed.

Hidden Worlds of Marine Microbes

NASA Astrophysics Data System (ADS)

Armbrust, E. V.

2016-12-01

Every drop of seawater contains fantastically diverse groups of microbes that control key biogeochemical processes in the ocean and determine the habitability of our planet. The challenge is to scale from this world of individual cells to ecosystem function and ultimately to ocean basin processes. Our work begins with microscopic marine diatoms because they are responsible for about twenty percent of the photosynthesis that occurs on Earth each year, they form the base of highly productive marine food webs, and they help regulate past and current fluxes of CO2 into the ocean. Diatoms evolved in a dilute environment where they are never free from the influences of other microbes. We explore the specifics of these interactions via model diatom/bacteria systems that can be manipulated in the laboratory - one includes an antagonistic bacterium that inhibits the growth of diatoms and a second includes a synergistic bacterium that enhances the growth of diatoms. We scale up from the cellular level to population-level interactions through use of our continuous flow cytometer, SeaFlow, which taps into a ship's seawater intake system to provide a continuous read-out of abundance, size and type of the smallest phytoplankton. We use this data to estimate division rates and mortality rates of these phytoplankton across thousands of kilometers of ocean basins. We tie these scales together with genomic approaches in both laboratory experiments and in open ocean field studies to document how interactions with the environment and between microbes drive specific adaptations. Our ultimate goal is to understand how microbial communities will respond to and will help shape future ocean conditions.

Tropical Ocean Surface Energy Balance Variability: Linking Weather to Climate Scales

NASA Technical Reports Server (NTRS)

Roberts, J. Brent; Clayson, Carol Anne

2013-01-01

Radiative and turbulent surface exchanges of heat and moisture across the atmosphere-ocean interface are fundamental components of the Earth s energy and water balance. Characterizing the spatiotemporal variability of these exchanges of heat and moisture is critical to understanding the global water and energy cycle variations, quantifying atmosphere-ocean feedbacks, and improving model predictability. These fluxes are integral components to tropical ocean-atmosphere variability; they can drive ocean mixed layer variations and modify the atmospheric boundary layer properties including moist static stability, thereby influencing larger-scale tropical dynamics. Non-parametric cluster-based classification of atmospheric and ocean surface properties has shown an ability to identify coherent weather regimes, each typically associated with similar properties and processes. Using satellite-based observational radiative and turbulent energy flux products, this study investigates the relationship between these weather states and surface energy processes within the context of tropical climate variability. Investigations of surface energy variations accompanying intraseasonal and interannual tropical variability often use composite-based analyses of the mean quantities of interest. Here, a similar compositing technique is employed, but the focus is on the distribution of the heat and moisture fluxes within their weather regimes. Are the observed changes in surface energy components dominated by changes in the frequency of the weather regimes or through changes in the associated fluxes within those regimes? It is this question that the presented work intends to address. The distribution of the surface heat and moisture fluxes is evaluated for both normal and non-normal states. By examining both phases of the climatic oscillations, the symmetry of energy and water cycle responses are considered.

Ice Melt, Sea Level Rise and Superstorms: Evidence from Paleoclimate Data, Climate Modeling, and Modern Observations that 2C Global Warming Could Be Dangerous

NASA Technical Reports Server (NTRS)

Hansen, J.; Sato, Makiko; Hearty, Paul; Ruedy, Reto; Kelley, Maxwell; Masson-Delmotte, Valerie; Russell, Gary; Tselioudis, George; Cao, Junji; Rignot, Eric;

Ice melt, sea level rise and superstorms: evidence from paleoclimate data, climate modeling, and modern observations that 2 °C global warming could be dangerous

NASA Astrophysics Data System (ADS)

Hansen, James; Sato, Makiko; Hearty, Paul; Ruedy, Reto; Kelley, Maxwell; Masson-Delmotte, Valerie; Russell, Gary; Tselioudis, George; Cao, Junji; Rignot, Eric; Velicogna, Isabella; Tormey, Blair; Donovan, Bailey; Kandiano, Evgeniya; von Schuckmann, Karina; Kharecha, Pushker; Legrande, Allegra N.; Bauer, Michael; Lo, Kwok-Wai

2016-03-01

We use numerical climate simulations, paleoclimate data, and modern observations to study the effect of growing ice melt from Antarctica and Greenland. Meltwater tends to stabilize the ocean column, inducing amplifying feedbacks that increase subsurface ocean warming and ice shelf melting. Cold meltwater and induced dynamical effects cause ocean surface cooling in the Southern Ocean and North Atlantic, thus increasing Earth's energy imbalance and heat flux into most of the global ocean's surface. Southern Ocean surface cooling, while lower latitudes are warming, increases precipitation on the Southern Ocean, increasing ocean stratification, slowing deepwater formation, and increasing ice sheet mass loss. These feedbacks make ice sheets in contact with the ocean vulnerable to accelerating disintegration. We hypothesize that ice mass loss from the most vulnerable ice, sufficient to raise sea level several meters, is better approximated as exponential than by a more linear response. Doubling times of 10, 20 or 40 years yield multi-meter sea level rise in about 50, 100 or 200 years. Recent ice melt doubling times are near the lower end of the 10-40-year range, but the record is too short to confirm the nature of the response. The feedbacks, including subsurface ocean warming, help explain paleoclimate data and point to a dominant Southern Ocean role in controlling atmospheric CO2, which in turn exercised tight control on global temperature and sea level. The millennial (500-2000-year) timescale of deep-ocean ventilation affects the timescale for natural CO2 change and thus the timescale for paleo-global climate, ice sheet, and sea level changes, but this paleo-millennial timescale should not be misinterpreted as the timescale for ice sheet response to a rapid, large, human-made climate forcing. These climate feedbacks aid interpretation of events late in the prior interglacial, when sea level rose to +6-9 m with evidence of extreme storms while Earth was less than 1 °C warmer than today. Ice melt cooling of the North Atlantic and Southern oceans increases atmospheric temperature gradients, eddy kinetic energy and baroclinicity, thus driving more powerful storms. The modeling, paleoclimate evidence, and ongoing observations together imply that 2 °C global warming above the preindustrial level could be dangerous. Continued high fossil fuel emissions this century are predicted to yield (1) cooling of the Southern Ocean, especially in the Western Hemisphere; (2) slowing of the Southern Ocean overturning circulation, warming of the ice shelves, and growing ice sheet mass loss; (3) slowdown and eventual shutdown of the Atlantic overturning circulation with cooling of the North Atlantic region; (4) increasingly powerful storms; and (5) nonlinearly growing sea level rise, reaching several meters over a timescale of 50-150 years. These predictions, especially the cooling in the Southern Ocean and North Atlantic with markedly reduced warming or even cooling in Europe, differ fundamentally from existing climate change assessments. We discuss observations and modeling studies needed to refute or clarify these assertions.

The South Asian Monsoon and the Tropospheric Biennial Oscillation.

NASA Astrophysics Data System (ADS)

Meehl, Gerald A.

1997-08-01

A mechanism is described that involves the south Asian monsoon as an active part of the tropospheric biennial oscillation (TBO) described in previous studies. This mechanism depends on coupled land-atmosphere-ocean interactions in the Indian sector, large-scale atmospheric east-west circulations in the Tropics, convective heating anomalies over Africa and the Pacific, and tropical-midlatitude interactions in the Northern Hemisphere. A key element for the monsoon role in the TBO is land-sea or meridional tropospheric temperature contrast, with area-averaged surface temperature anomalies over south Asia that are able to persist on a 1-yr timescale without the heat storage characteristics that contribute to this memory mechanism in the ocean. Results from a global coupled general circulation model show that soil moisture anomalies contribute to land-surface temperature anomalies (through latent heat flux anomalies) for only one season after the summer monsoon. A global atmospheric GCM in perpetual January mode is run with observed SSTs with specified convective heating anomalies to demonstrate that convective heating anomalies elsewhere in the Tropics associated with the coupled ocean-atmosphere biennial mechanism can contribute to altering seasonal midlatitude circulation. These changes in the midlatitude longwave pattern, forced by a combination of tropical convective heating anomalies over East Africa, Southeast Asia, and the western Pacific (in association with SST anomalies), are then able to maintain temperature anomalies over south Asia via advection through winter and spring to set up the land-sea meridional tropospheric temperature contrast for the subsequent monsoon. The role of the Indian Ocean, then, is to provide a moisture source and a low-amplitude coupled response component for meridional temperature contrast to help drive the south Asian monsoon. The role of the Pacific is to produce shifts in regionally coupled convection-SST anomalies. These regions are tied together and mutually interact via the large-scale east-west circulation in the atmosphere and contribute to altering midlatitude circulations as well. The coupled model results, and experiments with an atmospheric GCM that includes specified convective heating anomalies, suggest that the influence of south Asian snow cover in the monsoon is not a driving force by itself, but is symptomatic of the larger-scale shift in the midlatitude longwave pattern associated with tropical SST and convective heating anomalies.

Interannual Variability in Surface LW Fluxes Over the Tropical Oceans As Seen in ISCCP-FD and GEWEX SRB Data Sets

NASA Technical Reports Server (NTRS)

Robertson, F. R.; Lu, H.-I.

2005-01-01

One notable aspect of Earth s climate is that although the planet appears to be very close to radiative balance at top-of-atmosphere (TOA), the atmosphere itself and underlying surface are not. Profound exchanges of energy between the atmosphere and oceans, land and cryosphere occur over a range of time scales. Recent evidence from broadband satellite measurements suggests that even these TOA fluxes contain some detectable variations. Our ability to measure and reconstruct radiative fluxes at the surface and at the top of atmosphere is improving rapidly. In this work we will evaluate two recently released estimates of radiative fluxes, focusing primarily on surface estimates. The International Satellite Cloud Climatology Project FD radiative flux profiles are available from mid-1 983 to near present and have been constructed by driving the radiative transfer physics from the Goddard Institute for Space Studies (GISS) global model with ISCCP clouds and TOVS (TIROS Operational Vertical Sounder)thermodynamic profiles. Fu!l and clear sky SW and LW fluxes are produced. A similar product from the NASA/GEWEX Surface Radiation Budget Project using different radiative flux codes and thermodynamics from the NAS/Goddard Earth Observing System (GEOS-1) assimilation model makes a similar calculation of surface fluxes. However this data set currently extends only through 1995. Significant differences in both interannual variability as well as trends are found between among these data sets. For radiative fluxes these differences are traced to TOVS thermodynamic soundings used to drive the ISCCP-FD calculations. Errors in near surface temperature and precipitable water cascade into ISCCP upward and downward IR flux components, demonstrably affecting interannual variability. Revised estimates of clear-sky fluxes over ocean are made using statistical algorithms and water vapor from the (SSM/I) Special Sensor Microwave Imager. These calculations show strong near-surface water vapor feedback over the tropical oceans in association with SST changes. However, it is also shown that ISCCP longwave cloud forcing, common to both the ISCCP-FD and GEWEX SRB retrievals, is the main driver of a long-term decrease in net LW flux to the surface during the near-20 year period covered by these revised estimates.

Individual and population-level responses to ocean acidification.

PubMed

Harvey, Ben P; McKeown, Niall J; Rastrick, Samuel P S; Bertolini, Camilla; Foggo, Andy; Graham, Helen; Hall-Spencer, Jason M; Milazzo, Marco; Shaw, Paul W; Small, Daniel P; Moore, Pippa J

2016-01-29

Ocean acidification is predicted to have detrimental effects on many marine organisms and ecological processes. Despite growing evidence for direct impacts on specific species, few studies have simultaneously considered the effects of ocean acidification on individuals (e.g. consequences for energy budgets and resource partitioning) and population level demographic processes. Here we show that ocean acidification increases energetic demands on gastropods resulting in altered energy allocation, i.e. reduced shell size but increased body mass. When scaled up to the population level, long-term exposure to ocean acidification altered population demography, with evidence of a reduction in the proportion of females in the population and genetic signatures of increased variance in reproductive success among individuals. Such increased variance enhances levels of short-term genetic drift which is predicted to inhibit adaptation. Our study indicates that even against a background of high gene flow, ocean acidification is driving individual- and population-level changes that will impact eco-evolutionary trajectories.

Transforming Ocean Observations of the Carbon Budget, Acidification, Hypoxia, Nutrients, and Biological Productivity: a Global Array of Biogeochemical Argo Floats

NASA Astrophysics Data System (ADS)

Talley, L. D.; Johnson, K. S.; Claustre, H.; Boss, E.; Emerson, S. R.; Westberry, T. K.; Sarmiento, J. L.; Mazloff, M. R.; Riser, S.; Russell, J. L.

2017-12-01

Our ability to detect changes in biogeochemical (BGC) processes in the ocean that may be driven by increasing atmospheric CO2, as well as by natural climate variability, is greatly hindered by undersampling in vast areas of the open ocean. Argo is a major international program that measures ocean heat content and salinity with about 4000 floats distributed throughout the ocean, profiling to 2000 m every 10 days. Extending this approach to a global BGC-Argo float array, using recent, proven sensor technology, and in close synergy with satellite systems, will drive a transformative shift in observing and predicting the effects of climate change on ocean metabolism, carbon uptake, acidification, deoxygenation, and living marine resource management. BGC-Argo will add sensors for pH, oxygen, nitrate, chlorophyll, suspended particles, and downwelling irradiance, with sufficient accuracy for climate studies. Observing System Simulation Experiments (OSSEs) using BGC models indicate that 1000 BGC floats would provide sufficient coverage, hence equipping 1/4 of the Argo array. BGC-Argo (http://biogeochemical-argo.org) will enhance current sustained observational programs such as Argo, GO-SHIP, and long-term ocean time series. BGC-Argo will benefit from deployments on GO-SHIP vessels, which provide sensor verification. Empirically derived algorithms that relate the observed BGC float parameters to the carbon system parameters will provide global information on seasonal ocean-atmosphere carbon exchange. BGC Argo measurements could be paired with other emerging technology, such as pCO2 measurements from ships of opportunity and wave gliders, to extend and validate exchange estimates. BGC-Argo prototype programs already show the potential of a global observing system that can measure seasonal to decadal variability. Various countries have developed regional BGC arrays: Southern Ocean (SOCCOM), North Atlantic Subpolar Gyre (remOcean), Mediterranean (NAOS), the Kuroshio (INBOX), and Indian Ocean (IOBioArgo). As examples, bio-optical sensors are identifying regional anomalies in light attenuation/scattering, with implications for ocean productivity and carbon export; SOCCOM floats show high CO2 outgassing in the Antarctic Circumpolar Current, due to previously unmeasured winter fluxes.

Using the Environmental Intelligence Framework to Address Arctic Issues: A Case Study of Alaskan Fisheries and Ocean Acidification

NASA Astrophysics Data System (ADS)

Mathis, J. T.; Osborne, E.; Bamzai, A. S.; Starkweather, S.

2017-12-01

Profound environmental change in the Arctic region is driving an urgent need for faster and more efficient knowledge creation and delivery for residents of the Arctic as well as stakeholders around the globe. The overarching issues at play include environmental stewardship, community health and cultural survival. To effectively address these issues, the Interagency Arctic Research Policy Committee (IAPRC) recently established the Environmental Intelligence Collaboration Team (EICT) that integrates observing capabilities, modelling efforts and data management. Since its inception, the EICT has been working to create pathways to environmental knowledge that sustains end-to-end integration of research across the linked steps of data integration, environmental observing, predictive modelling, assessing responsiveness to stakeholder needs and ultimately providing decision support. The EICT is currently focusing on the carbon-climate aspect of environmental knowledge and identifing specific decision-making needs to meet policy goals for topics such as carbon emissions from permafrost thaw, increasing wildfire frequency and ocean acidification. As a case study, we applied the Environmental Intelligence framework to understanding the effects of ocean acidification in southern Alaska where there are critical commercial and subsistence fisheries. The results of this work revealed that there is currently a 5-month window of optimal growing conditions at a hatchery facility for many juvenile shellfish although that window is expected to close by 2040. The outcome of this work relates directly to fisheries management decisions and identifies the need for continued Environmental Intelligence collection to monitor and mitigate ocean acidification in the Alaskan region.

Modeling the intense 2012-2013 dense water formation event in the northwestern Mediterranean Sea: Evaluation with an ensemble simulation approach

NASA Astrophysics Data System (ADS)

Waldman, Robin; Somot, Samuel; Herrmann, Marine; Bosse, Anthony; Caniaux, Guy; Estournel, Claude; Houpert, Loic; Prieur, Louis; Sevault, Florence; Testor, Pierre

2017-02-01

The northwestern Mediterranean Sea is a well-observed ocean deep convection site. Winter 2012-2013 was an intense and intensely documented dense water formation (DWF) event. We evaluate this DWF event in an ensemble configuration of the regional ocean model NEMOMED12. We then assess for the first time the impact of ocean intrinsic variability on DWF with a novel perturbed initial state ensemble method. Finally, we identify the main physical mechanisms driving water mass transformations. NEMOMED12 reproduces accurately the deep convection chronology between late January and March, its location off the Gulf of Lions although with a southward shift and its magnitude. It fails to reproduce the Western Mediterranean Deep Waters salinification and warming, consistently with too strong a surface heat loss. The Ocean Intrinsic Variability modulates half of the DWF area, especially in the open-sea where the bathymetry slope is low. It modulates marginally (3-5%) the integrated DWF rate, but its increase with time suggests its impact could be larger at interannual timescales. We conclude that ensemble frameworks are necessary to evaluate accurately numerical simulations of DWF. Each phase of DWF has distinct diapycnal and thermohaline regimes: during preconditioning, the Mediterranean thermohaline circulation is driven by exchanges with the Algerian basin. During the intense mixing phase, surface heat fluxes trigger deep convection and internal mixing largely determines the resulting deep water properties. During restratification, lateral exchanges and internal mixing are enhanced. Finally, isopycnal mixing was shown to play a large role in water mass transformations during the preconditioning and restratification phases.

Ecogenomics and potential biogeochemical impacts of globally abundant ocean viruses.

PubMed

Roux, Simon; Brum, Jennifer R; Dutilh, Bas E; Sunagawa, Shinichi; Duhaime, Melissa B; Loy, Alexander; Poulos, Bonnie T; Solonenko, Natalie; Lara, Elena; Poulain, Julie; Pesant, Stéphane; Kandels-Lewis, Stefanie; Dimier, Céline; Picheral, Marc; Searson, Sarah; Cruaud, Corinne; Alberti, Adriana; Duarte, Carlos M; Gasol, Josep M; Vaqué, Dolors; Bork, Peer; Acinas, Silvia G; Wincker, Patrick; Sullivan, Matthew B

2016-09-29

Ocean microbes drive biogeochemical cycling on a global scale. However, this cycling is constrained by viruses that affect community composition, metabolic activity, and evolutionary trajectories. Owing to challenges with the sampling and cultivation of viruses, genome-level viral diversity remains poorly described and grossly understudied, with less than 1% of observed surface-ocean viruses known. Here we assemble complete genomes and large genomic fragments from both surface- and deep-ocean viruses sampled during the Tara Oceans and Malaspina research expeditions, and analyse the resulting 'global ocean virome' dataset to present a global map of abundant, double-stranded DNA viruses complete with genomic and ecological contexts. A total of 15,222 epipelagic and mesopelagic viral populations were identified, comprising 867 viral clusters (defined as approximately genus-level groups). This roughly triples the number of known ocean viral populations and doubles the number of candidate bacterial and archaeal virus genera, providing a near-complete sampling of epipelagic communities at both the population and viral-cluster level. We found that 38 of the 867 viral clusters were locally or globally abundant, together accounting for nearly half of the viral populations in any global ocean virome sample. While two-thirds of these clusters represent newly described viruses lacking any cultivated representative, most could be computationally linked to dominant, ecologically relevant microbial hosts. Moreover, we identified 243 viral-encoded auxiliary metabolic genes, of which only 95 were previously known. Deeper analyses of four of these auxiliary metabolic genes (dsrC, soxYZ, P-II (also known as glnB) and amoC) revealed that abundant viruses may directly manipulate sulfur and nitrogen cycling throughout the epipelagic ocean. This viral catalog and functional analyses provide a necessary foundation for the meaningful integration of viruses into ecosystem models where they act as key players in nutrient cycling and trophic networks.

Ecogenomics and potential biogeochemical impacts of globally abundant ocean viruses

NASA Astrophysics Data System (ADS)

2016-09-01

Ocean microbes drive biogeochemical cycling on a global scale. However, this cycling is constrained by viruses that affect community composition, metabolic activity, and evolutionary trajectories. Owing to challenges with the sampling and cultivation of viruses, genome-level viral diversity remains poorly described and grossly understudied, with less than 1% of observed surface-ocean viruses known. Here we assemble complete genomes and large genomic fragments from both surface- and deep-ocean viruses sampled during the Tara Oceans and Malaspina research expeditions, and analyse the resulting ‘global ocean virome’ dataset to present a global map of abundant, double-stranded DNA viruses complete with genomic and ecological contexts. A total of 15,222 epipelagic and mesopelagic viral populations were identified, comprising 867 viral clusters (defined as approximately genus-level groups). This roughly triples the number of known ocean viral populations and doubles the number of candidate bacterial and archaeal virus genera, providing a near-complete sampling of epipelagic communities at both the population and viral-cluster level. We found that 38 of the 867 viral clusters were locally or globally abundant, together accounting for nearly half of the viral populations in any global ocean virome sample. While two-thirds of these clusters represent newly described viruses lacking any cultivated representative, most could be computationally linked to dominant, ecologically relevant microbial hosts. Moreover, we identified 243 viral-encoded auxiliary metabolic genes, of which only 95 were previously known. Deeper analyses of four of these auxiliary metabolic genes (dsrC, soxYZ, P-II (also known as glnB) and amoC) revealed that abundant viruses may directly manipulate sulfur and nitrogen cycling throughout the epipelagic ocean. This viral catalog and functional analyses provide a necessary foundation for the meaningful integration of viruses into ecosystem models where they act as key players in nutrient cycling and trophic networks.

Mechanisms for Seasonal and Interannual Sea Surface Salinity Variability in the Indian Ocean

NASA Astrophysics Data System (ADS)

Köhler, J.; Stammer, D.; Serra, N.; Bryan, F.

2016-12-01

Space-borne salinity data in the Indian Ocean are analyzed over the period 2000-2015 based on data from the European Space Agency's (ESA) "Soil Moisture and Ocean Salinity" (SMOS) and the National Aeronautical Space Agency's (NASA) "Aquarius/SAC-D" missions. The seasonal variability is the dominant mode of sea surface salinity (SSS) variability in the Indian Ocean, accounting for more than 50% of salinity variance. Through a combined analysis of the satellite and ARGO data, dominant forcing terms for seasonal salinity changes are identified. It is found, that E-P controls seasonal salinity tendency in the western Indian Ocean, where the ITCZ has a strong seasonal cycle. In contrast, Ekman advection is the dominant term in the northern and eastern equatorial Indian Ocean. The influence of vertical processes on the salinity tendency is enhanced in coastal upwelling regions and south of the equator due to mid-ocean upwelling. Jointly those processes can explain most of the observed seasonal cycle with a correlation of 0.85 and an RMS difference of 0.07/month. However, the detailed composition of driving terms depends on underlying data products. In general, our study confirms previous results from Lisan Yu (2011); however, in the eastern Indian Ocean contrasting results indicate the leading role of meridional Ekman advection to the seasonal salinity tendency instead of surface external forces due to precipitation. The inferred dominant salinity budget terms are confirmed by results obtained from a high resolution NCAR Core model run driven by NCEP forcing fields. From an EOF analysis of the salinity fields after substracting the annual and semiannual cycle we found that the first EOF mode explains more than 20% of salinity variance. The first principal component of SSS EOF is correlated with the Indian Ocean Dipole Mode Index. Nevertheless the EOF pattern shows a meridional tripole structure, while the IOD describes a zonal SST dipole (Saji et al, 1999).

Spitting in the Ocean: Realistic Expectations of the Impact of Driver Alcohol Education and Rehabilitation Programs on the Problem of Drunk Driving.

ERIC Educational Resources Information Center

Waller, Patricia F.

Alcohol education and rehabilitation programs are widely accepted as an integral part of the enforcement of drunk driving laws; however, careful evaluations of these programs generally fail to show subsequent beneficial effects on traffic crashes. This fact is due in part to the many barriers to conducting sound program evaluations and in part to…

Atlantic meridional heat transports computed from balancing Earth's energy locally: AMOC and Ocean Meridional Heat Transport

DOE Office of Scientific and Technical Information (OSTI.GOV)

Trenberth, Kevin E.; Fasullo, John T.

The Atlantic Meridional Overturning Circulation plays a major role in moving heat and carbon around in the ocean. A new estimate of ocean heat transports for 2000 through 2013 throughout the Atlantic is derived. Top-of-atmosphere radiation is combined with atmospheric reanalyses to estimate surface heat fluxes and combined with vertically integrated ocean heat content to estimate ocean heat transport divergence as a residual. Atlantic peak northward ocean heat transports average 1.18 ± 0.13PW (1 sigma) at 15°N but vary considerably in latitude and time. Results agree well with observational estimates at 26.5°N from the RAPID array, but for 2004–2013 themore » meridional heat transport is 1.00 ± 0.11PW versus 1.23 ± 0.11PW for RAPID. In addition, these results have no hint of a trend, unlike the RAPID results. Finally, strong westerlies north of a meridian drive ocean currents and an ocean heat loss into the atmosphere that is exacerbated by a decrease in ocean heat transport northward.« less

Atlantic meridional heat transports computed from balancing Earth's energy locally: AMOC and Ocean Meridional Heat Transport

DOE PAGES

Trenberth, Kevin E.; Fasullo, John T.

2017-02-18

The Atlantic Meridional Overturning Circulation plays a major role in moving heat and carbon around in the ocean. A new estimate of ocean heat transports for 2000 through 2013 throughout the Atlantic is derived. Top-of-atmosphere radiation is combined with atmospheric reanalyses to estimate surface heat fluxes and combined with vertically integrated ocean heat content to estimate ocean heat transport divergence as a residual. Atlantic peak northward ocean heat transports average 1.18 ± 0.13PW (1 sigma) at 15°N but vary considerably in latitude and time. Results agree well with observational estimates at 26.5°N from the RAPID array, but for 2004–2013 themore » meridional heat transport is 1.00 ± 0.11PW versus 1.23 ± 0.11PW for RAPID. In addition, these results have no hint of a trend, unlike the RAPID results. Finally, strong westerlies north of a meridian drive ocean currents and an ocean heat loss into the atmosphere that is exacerbated by a decrease in ocean heat transport northward.« less

EarthLabs Modules: Engaging Students In Extended, Rigorous Investigations Of The Ocean, Climate and Weather

NASA Astrophysics Data System (ADS)

Manley, J.; Chegwidden, D.; Mote, A. S.; Ledley, T. S.; Lynds, S. E.; Haddad, N.; Ellins, K.

2016-02-01

EarthLabs, envisioned as a national model for high school Earth or Environmental Science lab courses, is adaptable for both undergraduate middle school students. The collection includes ten online modules that combine to feature a global view of our planet as a dynamic, interconnected system, by engaging learners in extended investigations. EarthLabs support state and national guidelines, including the NGSS, for science content. Four modules directly guide students to discover vital aspects of the oceans while five other modules incorporate ocean sciences in order to complete an understanding of Earth's climate system. Students gain a broad perspective on the key role oceans play in fishing industry, droughts, coral reefs, hurricanes, the carbon cycle, as well as life on land and in the seas to drive our changing climate by interacting with scientific research data, manipulating satellite imagery, numerical data, computer visualizations, experiments, and video tutorials. Students explore Earth system processes and build quantitative skills that enable them to objectively evaluate scientific findings for themselves as they move through ordered sequences that guide the learning. As a robust collection, EarthLabs modules engage students in extended, rigorous investigations allowing a deeper understanding of the ocean, climate and weather. This presentation provides an overview of the ten curriculum modules that comprise the EarthLabs collection developed by TERC and found at http://serc.carleton.edu/earthlabs/index.html. Evaluation data on the effectiveness and use in secondary education classrooms will be summarized.

77 FR 72863 - Ocean Transportation Intermediary License Applicants

Federal Register 2010, 2011, 2012, 2013, 2014

2012-12-06

... & D Transport, Inc. (NVO & OFF), 4869 Peavey Drive, Meridian, MS 39301. Officers: Uros Pejanovic, Vice... Nucete, Director. Application Type: New NVO & OFF License. Embarque Los Hidalgos LLC (NVO & OFF), 326...

76 FR 6135 - Ocean Transportation Intermediary License Applicants

Federal Register 2010, 2011, 2012, 2013, 2014

2011-02-03

.... Legend International Transport, LLC dba Prime Time Movers (NVO), 3310 Mandeville Canyon Road, Los Angeles... Type: License Transfer. Missouri Sea and Air Services, Inc. (NVO & OFF), 500 Meijer Drive, 107...

New insights into ocean sunfish (Mola mola) abundance and seasonal distribution in the northeast Atlantic.

PubMed

Breen, Patricia; Cañadas, Ana; Cadhla, Oliver Ó; Mackey, Mick; Scheidat, Meike; Geelhoed, Steve C V; Rogan, Emer; Jessopp, Mark

2017-05-17

The ocean sunfish, Mola mola, is the largest teleost fish in the world. Despite being found in all oceans of the world, little is known about its abundance and factors driving its distribution. In this study we provide the first abundance estimates for sunfish in offshore waters in the northeast Atlantic and the first record of extensive sunfish presence in these waters year-round. Abundance estimates and predictive distributions for sunfish in approximately 300,000 km² of the northeast Atlantic were derived from large scale offshore aerial surveys in 2015-2016 using distance sampling techniques. Generalized additive models of sunfish density were fitted to survey data from 17,360 km of line transect effort resulting in minimum abundance estimates of 12,702 (CI: 9,864-16,357) in the summer (Density = 0.043 ind/km²) and 8,223 individuals (CI: 6,178-10,946) (Density = 0.028 ind/km²) in the winter. Density surface models predicted seasonal shifts in distribution and highlighted the importance of the mixed layer depth, possibly related to thermoregulation following deep foraging dives. The abundance estimate and estimated daily consumption of 2,600 tonnes of jellyfish in the northeast Atlantic highlights the need to re-assess the importance of this species in the pelagic ecosystem, and its role in top-down control of jellyfish blooms.

Sources, variability and fate of freshwater in the Bellingshausen Sea, Antarctica

NASA Astrophysics Data System (ADS)

Regan, Heather C.; Holland, Paul R.; Meredith, Michael P.; Pike, Jennifer

2018-03-01

During the second half of the twentieth century, the Antarctic Peninsula was subjected to a rapid increase in air temperatures. This was accompanied by a reduction in sea ice extent, increased precipitation and a dramatic retreat of glaciers associated with an increase in heat flux from deep ocean water masses. Isotopic tracers have been used previously to investigate the relative importance of the different freshwater sources to the adjacent Bellingshausen Sea (BS), but the data coverage is strongly biased toward summer. Here we use a regional model to investigate the ocean's response to the observed changes in its different freshwater inputs (sea ice melt/freeze, precipitation, evaporation, iceberg/glacier melt, and ice shelf melt). The model successfully recreates BS water masses and performs well against available freshwater data. By tracing the sources and pathways of the individual components of the freshwater budget, we find that sea ice dominates seasonal changes in the total freshwater content and flux, but all sources make a comparable contribution to the annual-mean. Interannual variability is dominated by sea ice and precipitation. Decadal trends in the salinity and stratification of the ocean are investigated, and a 20-year surface freshening from 1992 to 2011 is found to be predominantly driven by decreasing autumn sea ice growth. These findings will help to elucidate the role of freshwater in driving circulation and water column structure changes in this climatically-sensitive region.

Glacial cycles drive variations in the production of oceanic crust

NASA Astrophysics Data System (ADS)

Crowley, J. W.; Katz, R. F.; Langmuir, C. H.; Huybers, P. J.

2013-12-01

Changes in sea level accompanying glacial cycles affect the static pressure within the asthenosphere; these variations could modulate melting rates beneath the mid-ocean ridge system as well as crustal thickness. These effects can be investigated and quantified using models of ridges based on conservation of mass, momentum, energy, and composition for two phases (magma & mantle) and two thermodynamic components (enriched & depleted). The models predict that the sensitivity of crustal thickness to oscillations in sea-level depends on the period of oscillation, the spreading rate of the ridge, and the assumed permeability scale of the melting regime. In contrast to previous studies (Huybers & Langmuir, 2009 and Lund & Asimow, 2011), the new results indicate that effects are larger for ridges with faster spreading rates. They also show that the dominant period of variations in crustal thickness changes with spreading rate and permeability. Sea-level variations with periods in the range of 10 ky - 100 ky can result in significant changes in crustal thickness that are orders of magnitude larger than the sea-level variations that drive them. Accurately modelling this process requires the inclusion of two previously unaccounted for processes: (1) determining the volume of the melting regime that is consistent with the ridge spreading rate and (2) properly treating the transport of melt. These enable us to capture the non-linear dependencies on spreading rate and other model parameters. Spectral analysis of bathymetry at two ridge segments that have a symmetric bathymetric signal and hence are undisturbed by off-axis volcanism or ridge jumps reveals the presence of variability at frequencies associated with precession, obliquity, and the 100 ky glacial/inter-glacial variability. Furthermore, the faster spreading ridge has larger amplitude responses to changes in sea level and shows a proportionately greater response at higher frequencies. These observations reinforce the possible links among climate cycles at the surface, mantle melting at depth and the crustal fabric of the sea floor.

Air-Sea Interaction Processes in Low and High-Resolution Coupled Climate Model Simulations for the Southeast Pacific

NASA Astrophysics Data System (ADS)

Porto da Silveira, I.; Zuidema, P.; Kirtman, B. P.

2017-12-01

The rugged topography of the Andes Cordillera along with strong coastal upwelling, strong sea surface temperatures (SST) gradients and extensive but geometrically-thin stratocumulus decks turns the Southeast Pacific (SEP) into a challenge for numerical modeling. In this study, hindcast simulations using the Community Climate System Model (CCSM4) at two resolutions were analyzed to examine the importance of resolution alone, with the parameterizations otherwise left unchanged. The hindcasts were initialized on January 1 with the real-time oceanic and atmospheric reanalysis (CFSR) from 1982 to 2003, forming a 10-member ensemble. The two resolutions are (0.1o oceanic and 0.5o atmospheric) and (1.125o oceanic and 0.9o atmospheric). The SST error growth in the first six days of integration (fast errors) and those resulted from model drift (saturated errors) are assessed and compared towards evaluating the model processes responsible for the SST error growth. For the high-resolution simulation, SST fast errors are positive (+0.3oC) near the continental borders and negative offshore (-0.1oC). Both are associated with a decrease in cloud cover, a weakening of the prevailing southwesterly winds and a reduction of latent heat flux. The saturated errors possess a similar spatial pattern, but are larger and are more spatially concentrated. This suggests that the processes driving the errors already become established within the first week, in contrast to the low-resolution simulations. These, instead, manifest too-warm SSTs related to too-weak upwelling, driven by too-strong winds and Ekman pumping. Nevertheless, the ocean surface tends to be cooler in the low-resolution simulation than the high-resolution due to a higher cloud cover. Throughout the integration, saturated SST errors become positive and could reach values up to +4oC. These are accompanied by upwelling dumping and a decrease in cloud cover. High and low resolution models presented notable differences in how SST errors variability drove atmospheric changes, especially because the high resolution is sensitive to resurgence regions. This allows the model to resolve cloud heights and establish different radiative feedbacks.

Availability of free oxygen in deep bottom water of some Archean-Early Paleoproterozoic ocean basins as derived from iron formation facies analyses

NASA Astrophysics Data System (ADS)

Beukes, N. J.; Smith, A.

2013-12-01

Archean to Early Paleoproterozoic ocean basins are commonly, although not exclusively, depicted as rather static systems; either permanently stratified with shallow mixed oxygenated water overlying anoxic deep water or with a totally anoxic water column. The anoxic water columns are considered enriched in dissolved ferrous iron derived from hydrothermal plume activity. These sourced deposition of iron formations through precipitation of mainly ferrihydrite via reaction with free oxygen in the stratified model or anaerobic iron oxidizing photoautotrophs in the anoxic model. However, both these models face a simple basic problem if detailed facies reconstructions of deepwater microbanded iron formations (MIFs) are considered. In such MIFs it is common that the deepest water and most distal facies is hematite rich followed shoreward by magnetite, iron silicate and siderite facies iron formation. Examples of such facies relations are known from jaspilitic iron formation of the ~3,2 Ga Fig Tree Group (Barberton Mountainland), ~ 2,95 Ga iron formations of the Witwatersrand-Mozaan basin and the ~2,5 Ga Kuruman Iron Formation, Transvaal Supergroup, South Africa. Facies relations of these MIFs with associated siliciclastics or carbonates also indicate that the upper water columns of the basins, down to below wave base, were depleted in iron favoring anoxic-oxic stratification rather than total anoxia. In the MIFs it can be shown that hematite in the distal facies represents the earliest formed diagenetic mineral; most likely crystallized from primary ferrihydrite. The problem is one of how ferrihydrite could have been preserved on the ocean floor if it was in direct contact with reducing ferrous deep bottom water. Rather dissolved ferrous iron would have reacted with ferrihydrite to form diagenetic magnetite. This dilemma is resolved if in the area of deepwater hematite MIF deposition, the anoxic ferrous iron enriched plume was detached from the basin floor due to buoyancy in slightly oxygenated cold deep ocean water. Ferrihydrite, precipitated along the oxic-anoxic interface along the bottom of the buoyant plume could then settle to the floor of the basin without interference of dissolved ferrous iron. This model requires that oxygen, derived from photosynthesis in shallow water, circulated down to deep water creating a slightly oxygenated ocean basin system invaded by buoyant anoxic ferrous plumes. In areas where these plumes came in contact with the basin floor, magnetite and/or carbonate facies iron formation formed; the latter in areas of highest organic carbon influx. Extensive glacial diamictites in the Witwatersrand-Mozaan basin argues for climatic zonation in the Mesoarchean driving deep ocean currents. This model may explain why the rise of oxygen in the atmosphere was so long delayed after development of oxygenic photosynthesis; simply because in the dynamic ocean system oxygen could come into contact with much larger volumes of reduced species in the water column and along the ocean floor than in a static stratified system. It also impacts on reconstruction of microbial communities in Archean oceans.

77 FR 1936 - Ocean Transportation Intermediary License; Applicants

Federal Register 2010, 2011, 2012, 2013, 2014

2012-01-12

...), 9333 Elm Vista Drive, 9, Downey, CA 90242, Officer: Cynthia Choi, CEO/CFO/Secretary, (Qualifying.... Steele Logistics, LLC (NVO), 10722 La Cienega Blvd., Inglewood, CA 90304, Officer: Rene N. Steele, Member...

The USGODAE Monterey Data Server

NASA Astrophysics Data System (ADS)

Sharfstein, P. J.; Dimitriou, D.; Hankin, S. C.

2004-12-01

With oversight from the U.S. Global Ocean Data Assimilation Experiment (GODAE) Steering Committee and funding from the Office of Naval Research, the USGODAE Monterey Data Server has been established at the Fleet Numerical Meteorology and Oceanography Center (FNMOC) as an explicit U.S. contribution to GODAE. Support of the Monterey Data Server is accomplished by a cooperative effort between FNMOC and NOAA's Pacific Marine Environmental Laboratory (PMEL) in the on-going development of the server and the support of a collaborative network of GODAE assimilation groups. This server hosts near real-time in-situ oceanographic data, atmospheric forcing fields suitable for driving ocean models, and unique GODAE data sets, including demonstration ocean model products. GODAE is envisioned as a global system of observations, communications, modeling and assimilation, which will deliver regular, comprehensive information on the state of the oceans in a way that will promote and engender wide utility and availability of this resource for maximum benefit to society. It aims to make ocean monitoring and prediction a routine activity in a manner similar to weather forecasting. GODAE will contribute to an information system for the global ocean that will serve interests from climate and climate change to ship routing and fisheries. The USGODAE Server is developed and operated as a prototypical node for this global information system. Because of the broad range and diverse formats of data used by the GODAE community, presenting data with a consistent interface and ensuring its availability in standard formats is a primary challenge faced by the USGODAE Server project. To this end, all USGODAE data sets are available via HTTP and FTP. In addition, USGODAE data are served using Local Data Manager (LDM), THREDDS cataloging, OPeNDAP, and Live Access Server (LAS) from PMEL. Every effort is made to serve USGODAE data through the standards specified by the National Virtual Ocean Data System (NVODS) and the Integrated Ocean Observing System Data Management and Communications (IOOS/DMAC). To provide surface forcing, fluxes, and boundary conditions for ocean model research, USGODAE serves global data from the Navy Operational Global Atmospheric Prediction System (NOGAPS) and regional data from the Coupled Ocean/Atmosphere Mesoscale Prediction System (COAMPS). Global meteorological data and observational data from the FNMOC Ocean QC process are posted in near real-time to USGODAE. These include T/S profiles, in-situ and satellite sea surface temperature (SST), satellite altimetry, and SSM/I sea ice. They contain all of the unclassified in-situ and satellite observations used to initialize the FNMOC NOGAPS model. Also, the Naval Oceanographic Office provides daily satellite SST and SSH retrievals to USGODAE. The USGODAE Server functions as one of two Argo Global Data Assembly Centers (GDACs), hosting the complete collection of quality-controlled Argo T/S profiling float data. USGODAE Argo data are served through OPeNDAP and LAS, providing complete integration into NVODS and the IOOS/DMAC. Due to its high reliability, ease of data access, and increasing breadth of data, the USGODAE Server is becoming an invaluable resource for both the GODAE community and the general oceanographic community. Continued integration of model, forcing, and in-situ data sets from providers throughout the world is making the USGODAE Monterey Data Server a key part of the international GODAE project.

The roles of vertical mixing, solar radiation, and wind stress in a model simulation of the sea surface temperature seasonal cycle in the tropical Pacfic Ocean

NASA Technical Reports Server (NTRS)

Chen, Dake; Busalacchi, Antonio J.; Rothstein, Lewis M.

1994-01-01

The climatological seasonal cycle of sea surface temperature (SST) in the tropical Pacific is simulated using a newly developed upper ocean model. The roles of vertical mixing, solar radiation, and wind stress are investigated in a hierarchy of numerical experiments with various combinations of vertical mixing algorithms and surface-forcing products. It is found that the large SST annual cycle in the eastern equatorial Pacific is, to a large extent, controlled by the annually varying mixed layer depth which, in turn, is mainly determined by the competing effects of solar radiation and wind forcing. With the application of our hybrid vertical mixing scheme the model-simulated SST annual cycle is much improved in both amplitude and phase as compared to the case of a constant mixed layer depth. Beside the strong effects on vertical mixing, solar radiation is the primary heating term in the surface layer heat budget, and wind forcing influences SST by driving oceanic advective processes that redistribute heat in the upper ocean. For example, the SST seasonal cycle in the western Pacific basically follows the semiannual variation of solar heating, and the cycle in the central equatorial region is significantly affected by the zonal advective heat flux associated with the seasonally reversing South Equatorial Current. It has been shown in our experiments that the amount of heat flux modification needed to eliminate the annual mean SST errors in the model is, on average, no larger than the annual mean uncertainties among the various surface flux products used in this study. Whereas a bias correction is needed to account for remaining uncertainties in the annual mean heat flux, this study demonstrates that with proper treatment of mixed layer physics and realistic forcing functions the seasonal variability of SST is capable of being simulated successfully in response to external forcing without relying on a relaxation or damping formulation for the dominant surface heat flux contributions.

Erosion of volcanic ocean islands: insights from modeling, topographic analyses, and cosmogenic exposure dating

NASA Astrophysics Data System (ADS)

Huppert, K.; Perron, J. T.; Ferrier, K.; Mukhopadhyay, S.; Rosener, M.; Douglas, M.

2016-12-01

With homogeneous bedrock, dramatic rainfall gradients, paleoshorelines, and datable remnant topography, volcanic ocean islands provide an exceptional natural experiment in landscape evolution. Analyses traversing gradients in island climate and bedrock age have the potential to advance our understanding of landscape evolution in a diverse range of continental settings. However, as small, conical, dominantly subsiding, and initially highly permeable landmasses, islands are unique, and it remains unclear how these properties influence their erosional history. We use a landscape evolution model and observations from the Hawaiian island of Kaua'i and other islands to characterize the topographic evolution of volcanic ocean islands. We present new measurements of helium-3 concentrations in detrital olivine from 20 rivers on Kaua'i. These measurements indicate that minimum erosion rates over the past 3 to 48 kyr are on average 2.6 times faster than erosion rates averaged over the past 3.9 to 4.4 Myr estimated from the volume of river canyons. This apparent acceleration of erosion rates on Kaua'i is consistent with observations on other islands; erosion rates estimated from the volume of river canyons on 31 islands worldwide, combined with observations of minimal incision on young island volcanoes, suggest a progressive increase in erosion rates over the first few million years of island landscape development. Using a landscape evolution model, we perform a set of experiments to quantify the contribution of subsidence, climate change, and initial geometry to changes in island erosion rates through time. We base these experiments on the evolution of Kaua'i, and we use measured erosion rates and the observed topography to calibrate the model. We find that progressive steepening of island topography by canyon incision drives an acceleration of erosion rates over time. Increases in mean channel and hillslope gradient with island age in the global compilation suggest this may be a general trend in the topographic evolution of volcanic ocean islands.

Atlantic Induced Pan-tropical Climate Variability in the Upper-ocean and Atmosphere

NASA Astrophysics Data System (ADS)

Li, X.; Xie, S. P.; Gille, S. T.; Yoo, C.

2016-02-01

During the last three decades, tropical sea surface temperature (SST) exhibited dipole-like trends, with warming over the tropical Atlantic and Indo-Western Pacific but cooling over the Eastern Pacific. The Eastern Pacific cooling has recently been identified as a driver of the global warming hiatus. Previous studies revealed atmospheric bridges between the tropical Pacific, Atlantic, and Indian Ocean, which could potentially contribute to this zonally asymmetric SST pattern. However, the mechanisms and the interactions between these teleconnections remain unclear. To investigate these questions, we performed a `pacemaker' simulation by restoring the tropical Atlantic SST changes in a state-of-the-art climate model - the CESM1. Results show that the Atlantic plays a key role in initiating the tropical-wide teleconnections, and the Atlantic-induced anomalies contribute 55%-75% of the total tropical SST and circulation changes during the satellite era. A hierarchy of oceanic and atmospheric models are then used to investigate the physical mechanisms of these teleconnections: the Atlantic warming enhances atmospheric deep convection, drives easterly wind anomalies over the Indo-Western Pacific through the Kelvin wave, and westerly anomalies over the eastern Pacific as Rossby waves, in line with Gill's solution (Fig1a). These wind changes induce an Indo-Western Pacific warming via the wind-evaporation-SST effect, and this warming intensifies the La Niña-type response in the upper Pacific Ocean by enhancing the easterly trade winds and through the Bjerknes ocean-dynamical processes (Fig1b). The teleconnection finally develops into a tropical-wide SST dipole pattern with an enhanced trade wind and Walker circulation, similar as the observed changes during the satellite era. This mechanism reveals that the tropical ocean basins are more tightly connected than previously thought, and the Atlantic plays a key role in the tropical climate pattern formation and further the global warming hiatus. The tropical Atlantic warming is likely due to radiative forcing and Atlantic meridional overturning circulation (AMOC). Our study suggests that the AMOC may force the decadal variability of the tropical ocean and atmosphere, and thus contributes to the decadal predictability of the global climate.

The Effect of Changes in the Hadley Circulation on Oceanic Oxygen Minimum Zones

NASA Astrophysics Data System (ADS)

De La Cruz Tello, G.; Ummenhofer, C.; Karnauskas, K. B.

2014-12-01

Recent research argued that the Hadley circulation (HC) is composed of three regional cells located at the eastern edges of the ocean basins, rather than a single, globe-encircling cell as the classic textbook view suggests. The HC is expected to expand in concert with global warming, which means that the dry regions beneath the descending branches of the HC are projected to become even drier. Changes in the HC are thus likely to impact freshwater resources on land, as well as the underlying ocean in the subtropics. The eastern edges of ocean basins are characterized by oxygen minimum zones (OMZs), which are regions of very low oxygen concentrations. They affect marine life, as many animals cannot handle the stress caused by such conditions. OMZs have expanded and shoaled in the last 50 years, and they are expected to continue to do so as global climate changes. The purpose of this research is to find links between the projected changes in OMZs and the HC. The National Center for Atmospheric Research (NCAR) Community Earth System Model 1.0 (CESM), Representative Concentration Pathways 8.5 (RCP8.5) experiment with a resolution of 0.9 by 1.25 degrees, which formed part of the Coupled Model Intercomparison Project phase 5 (CMIP5), was used for this analysis. Meridional winds and oceanic oxygen concentrations were the primarily analyzed variables. Latitudinal ocean oxygen slices demonstrate the OMZs' location along the eastern edges of ocean basins. Meridional winds overlayed with oxygen concentration are consistent with the idea that surface meridional 'Hadleywise flow' (i.e., towards the equator at the surface and towards the poles aloft) and OMZs are linked through changes in upwelling. Area-averaged time series spanning the historical period through to the end of the 21st century with RCP8.5 confirm that future changes in OMZs and the HC may be connected. Further research could lead to improved understanding of the factors that drive changes in both, which could help anticipate and mitigate the consequences discussed previously.

Optimal Asset Distribution for Environmental Assessment and Forecasting Based on Observations, Adaptive Sampling, and Numerical Prediction

DTIC Science & Technology

2012-09-30

and Forecasting Based on Observations, Adaptive Sampling, and Numerical Prediction Steven R. Ramp Soliton Ocean Services, Inc. 691 Country Club... Soliton Ocean Services, Inc,691 Country Club Drive,Monterey,CA,93924 8. PERFORMING ORGANIZATION REPORT NUMBER 9. SPONSORING/MONITORING AGENCY NAME(S...shortwave. The results show that the incoming shortwave radiation was the dominant term, even when averaged over the dark hours, which accounts

Lateral Coherence and Mixing in the Coastal Ocean: Adaptive Sampling using Gliders

DTIC Science & Technology

2011-09-30

Coherence and Mixing in the Coastal Ocean: Adaptive Sampling using Gliders R. Kipp Shearman Jonathan D. Nash James N. Moum John A. Barth College of...These structures evolve yet are often persistent on O (3 day) timescales, so are ideally suited to be adaptively sampled by autonomous gliders that...processes driving lateral dispersion, we plan to deploy 4 AUV gliders to perform intensive, adaptive surveys. Newly-enhanced to measure turbulent mixing

Polar Marine Microorganisms and Climate Change.

PubMed

Verde, C; Giordano, D; Bellas, C M; di Prisco, G; Anesio, A M

2016-01-01

The large diversity of marine microorganisms harboured by oceans plays an important role in planet sustainability by driving globally important biogeochemical cycles; all primary and most secondary production in the oceans is performed by microorganisms. The largest part of the planet is covered by cold environments; consequently, cold-adapted microorganisms have crucial functional roles in globally important environmental processes and biogeochemical cycles cold-adapted extremophiles are a remarkable model to shed light on the molecular basis of survival at low temperature. The indigenous populations of Antarctic and Arctic microorganisms are endowed with genetic and physiological traits that allow them to live and effectively compete at the temperatures prevailing in polar regions. Some genes, e.g. glycosyltransferases and glycosylsynthetases involved in the architecture of the cell wall, may have been acquired/retained during evolution of polar strains or lost in tropical strains. This present work focusses on temperature and its role in shaping microbial adaptations; however, in assessing the impacts of climate changes on microbial diversity and biogeochemical cycles in polar oceans, it should not be forgotten that physiological studies need to include the interaction of temperature with other abiotic and biotic factors. © 2016 Elsevier Ltd All rights reserved.

The relationship between Arabian Sea upwelling and Indian Monsoon revisited in a high resolution ocean simulation

NASA Astrophysics Data System (ADS)

Yi, Xing; Hünicke, Birgit; Tim, Nele; Zorita, Eduardo

2018-01-01

Studies based on sediment records, sea-surface temperature and wind suggest that upwelling along the western coast of Arabian Sea is strongly affected by the Indian summer Monsoon. We examine this relationship directly in an eddy-resolving global ocean simulation STORM driven by atmospheric reanalysis over the last 61 years. With its very high spatial resolution (10 km), STORM allows us to identify characteristics of the upwelling system. We analyse the co-variability between upwelling and meteorological and oceanic variables from 1950 to 2010. The analysis reveals high interannual correlations between coastal upwelling and along-shore wind-stress (r = 0.73) as well as with sea-surface temperature (r = -0.83). However, the correlation between the upwelling and the Monsoon is small. We find an atmospheric circulation pattern different from the one that drives the Monsoon as the main modulator of the upwelling variability. In spite of this, the patterns of temperature anomalies that are either linked to Arabian Sea upwelling or to the Monsoon are spatially quite similar, although the physical mechanisms of these links are different. In addition, no long-term trend is detected in our modelled upwelling in the Arabian Sea.

Dynamic Downscaling of Seasonal Simulations over South America.

NASA Astrophysics Data System (ADS)

Misra, Vasubandhu; Dirmeyer, Paul A.; Kirtman, Ben P.

2003-01-01

In this paper multiple atmospheric global circulation model (AGCM) integrations at T42 spectral truncation and prescribed sea surface temperature were used to drive regional spectral model (RSM) simulations at 80-km resolution for the austral summer season (January-February-March). Relative to the AGCM, the RSM improves the ensemble mean simulation of precipitation and the lower- and upper-level tropospheric circulation over both tropical and subtropical South America and the neighboring ocean basins. It is also seen that the RSM exacerbates the dry bias over the northern tip of South America and the Nordeste region, and perpetuates the erroneous split intertropical convergence zone (ITCZ) over both the Pacific and Atlantic Ocean basins from the AGCM. The RSM at 80-km horizontal resolution is able to reasonably resolve the Altiplano plateau. This led to an improvement in the mean precipitation over the plateau. The improved resolution orography in the RSM did not substantially change the predictability of the precipitation, surface fluxes, or upper- and lower-level winds in the vicinity of the Andes Mountains from the AGCM. In spite of identical convective and land surface parameterization schemes, the diagnostic quantities, such as precipitation and surface fluxes, show significant differences in the intramodel variability over oceans and certain parts of the Amazon River basin (ARB). However, the prognostic variables of the models exhibit relatively similar model noise structures and magnitude. This suggests that the model physics are in large part responsible for the divergence of the solutions in the two models. However, the surface temperature and fluxes from the land surface scheme of the model [Simplified Simple Biosphere scheme (SSiB)] display comparable intramodel variability, except over certain parts of ARB in the two models. This suggests a certain resilience of predictability in SSiB (over the chosen domain of study) to variations in horizontal resolution. It is seen in this study that the summer precipitation over tropical and subtropical South America is highly unpredictable in both models.

Montane ecosystem productivity responds more to global circulation patterns than climatic trends.

PubMed

Desai, A R; Wohlfahrt, G; Zeeman, M J; Katata, G; Eugster, W; Montagnani, L; Gianelle, D; Mauder, M; Schmid, H-P

2016-02-01

Regional ecosystem productivity is highly sensitive to inter-annual climate variability, both within and outside the primary carbon uptake period. However, Earth system models lack sufficient spatial scales and ecosystem processes to resolve how these processes may change in a warming climate. Here, we show, how for the European Alps, mid-latitude Atlantic ocean winter circulation anomalies drive high-altitude summer forest and grassland productivity, through feedbacks among orographic wind circulation patterns, snowfall, winter and spring temperatures, and vegetation activity. Therefore, to understand future global climate change influence to regional ecosystem productivity, Earth systems models need to focus on improvements towards topographic downscaling of changes in regional atmospheric circulation patterns and to lagged responses in vegetation dynamics to non-growing season climate anomalies.

Montane ecosystem productivity responds more to global circulation patterns than climatic trends

NASA Astrophysics Data System (ADS)

Desai, A. R.; Wohlfahrt, G.; Zeeman, M. J.; Katata, G.; Eugster, W.; Montagnani, L.; Gianelle, D.; Mauder, M.; Schmid, H.-P.

2016-02-01

Regional ecosystem productivity is highly sensitive to inter-annual climate variability, both within and outside the primary carbon uptake period. However, Earth system models lack sufficient spatial scales and ecosystem processes to resolve how these processes may change in a warming climate. Here, we show, how for the European Alps, mid-latitude Atlantic ocean winter circulation anomalies drive high-altitude summer forest and grassland productivity, through feedbacks among orographic wind circulation patterns, snowfall, winter and spring temperatures, and vegetation activity. Therefore, to understand future global climate change influence to regional ecosystem productivity, Earth systems models need to focus on improvements towards topographic downscaling of changes in regional atmospheric circulation patterns and to lagged responses in vegetation dynamics to non-growing season climate anomalies.

Mesoscale eddies drive increased silica export in the subtropical Pacific Ocean.

PubMed

Benitez-Nelson, Claudia R; Bidigare, Robert R; Dickey, Tommy D; Landry, Michael R; Leonard, Carrie L; Brown, Susan L; Nencioli, Francesco; Rii, Yoshimi M; Maiti, Kanchan; Becker, Jamie W; Bibby, Thomas S; Black, Wil; Cai, Wei-Jun; Carlson, Craig A; Chen, Feizhou; Kuwahara, Victor S; Mahaffey, Claire; McAndrew, Patricia M; Quay, Paul D; Rappé, Michael S; Selph, Karen E; Simmons, Melinda P; Yang, Eun Jin

2007-05-18

Mesoscale eddies may play a critical role in ocean biogeochemistry by increasing nutrient supply, primary production, and efficiency of the biological pump, that is, the ratio of carbon export to primary production in otherwise nutrient-deficient waters. We examined a diatom bloom within a cold-core cyclonic eddy off Hawaii. Eddy primary production, community biomass, and size composition were markedly enhanced but had little effect on the carbon export ratio. Instead, the system functioned as a selective silica pump. Strong trophic coupling and inefficient organic export may be general characteristics of community perturbation responses in the warm waters of the Pacific Ocean.

Impacts of continental arcs on global carbon cycling and climate

NASA Astrophysics Data System (ADS)

Lee, C. T.; Jiang, H.; Carter, L.; Dasgupta, R.; Cao, W.; Lackey, J. S.; Lenardic, A.; Barnes, J.; McKenzie, R.

2017-12-01

On myr timescales, climatic variability is tied to variations in atmospheric CO2, which in turn is driven by geologic sources of CO2 and modulated by the efficiency of chemical weathering and carbonate precipitation (sinks). Long-term variability in CO2 has largely been attributed to changes in mid-ocean ridge inputs or the efficiency of global weathering. For example, the Cretaceous greenhouse is thought to be related to enhanced oceanic crust production, while the late Cenozoic icehouse is attributed to enhanced chemical weathering associated with the Himalayan orogeny. Here, we show that continental arcs may play a more important role in controlling climate, both in terms of sources and sinks. Continental arcs differ from island arcs and mid-ocean ridges in that the continental plate through which arc magmas pass may contain large amounts of sedimentary carbonate, accumulated over the history of the continent. Interaction of arc magmas with crustal carbonates via assimilation, reaction or heating can significantly add to the mantle-sourced CO2 flux. Detrital zircons and global mapping of basement rocks shows that the length of continental arcs in the Cretaceous was more than twice that in the mid-Cenozoic; maps also show many of these arcs intersected crustal carbonates. The increased length of continental arc magmatism coincided with increased oceanic spreading rates, placing convergent margins into compression, which favors continental arcs. Around 50 Ma, however, nearly all the continental arcs in Eurasia and North America terminated as India collided with Eurasia and the western Pacific rolled back, initiating the Marianas-Tonga-Kermadec intra-oceanic subduction complex and possibly leading to a decrease in global CO2 production. Meanwhile, extinct continental arcs continued to erode, resulting in regionally enhanced chemical weathering unsupported by magmatic fluxes of CO2. Continental arcs, during their magmatic lifetimes, are thus a source of CO2, driving greenhouse climates, but after they die magmatically, they remain geomorphically active and become a net CO2 sink, helping to drive climate towards cooler conditions. Tectonic oscillations that drive fluctuations in the activity of continental arcs thus may be responsible for greenhouse-icehouse oscillations in the Phanerozoic.

Glacial-interglacial atmospheric CO2 change: a possible "standing volume" effect on deep-ocean carbon sequestration

NASA Astrophysics Data System (ADS)

Skinner, L. C.

2009-09-01

So far, the exploration of possible mechanisms for glacial atmospheric CO2 drawdown and marine carbon sequestration has tended to focus on dynamic or kinetic processes (i.e. variable mixing-, equilibration- or export rates). Here an attempt is made to underline instead the possible importance of changes in the standing volumes of intra-oceanic carbon reservoirs (i.e. different water-masses) in influencing the total marine carbon inventory. By way of illustration, a simple mechanism is proposed for enhancing the marine carbon inventory via an increase in the volume of relatively cold and carbon-enriched deep water, analogous to modern Lower Circumpolar Deep Water (LCDW), filling the ocean basins. A set of simple box-model experiments confirm the expectation that a deep sea dominated by an expanded LCDW-like watermass holds more CO2, without any pre-imposed changes in ocean overturning rate, biological export or ocean-atmosphere exchange. The magnitude of this "standing volume effect" (which operates by boosting the solubility- and biological pumps) might be as large as the contributions that have previously been attributed to carbonate compensation, terrestrial biosphere reduction or ocean fertilisation for example. By providing a means of not only enhancing but also driving changes in the efficiency of the biological- and solubility pumps, this standing volume mechanism may help to reduce the amount of glacial-interglacial CO2 change that remains to be explained by other mechanisms that are difficult to assess in the geological archive, such as reduced mass transport or mixing rates in particular. This in turn could help narrow the search for forcing conditions capable of pushing the global carbon cycle between glacial and interglacial modes.

Macronutrient supply, uptake and recycling in the coastal ocean of the west Antarctic Peninsula

NASA Astrophysics Data System (ADS)

Henley, Sian F.; Tuerena, Robyn E.; Annett, Amber L.; Fallick, Anthony E.; Meredith, Michael P.; Venables, Hugh J.; Clarke, Andrew; Ganeshram, Raja S.

2017-05-01

Nutrient supply, uptake and cycling underpin high primary productivity over the continental shelf of the west Antarctic Peninsula (WAP). Here we use a suite of biogeochemical and isotopic data collected over five years in northern Marguerite Bay to examine these macronutrient dynamics and their controlling biological and physical processes in the WAP coastal ocean. We show pronounced nutrient drawdown over the summer months by primary production which drives a net seasonal nitrate uptake of 1.83 mol N m-2 yr-1, equivalent to net carbon uptake of 146 g C m-2 yr-1. High primary production fuelled primarily by deep-sourced macronutrients is diatom-dominated, but non-siliceous phytoplankton also play a role. Strong nutrient drawdown in the uppermost surface ocean has the potential to cause transient nitrogen limitation before nutrient resupply and/or regeneration. Interannual variability in nutrient utilisation corresponds to winter sea ice duration and the degree of upper ocean mixing, implying susceptibility to physical climate change. The nitrogen isotope composition of nitrate (δ15NNO3) shows a utilisation signal during the growing seasons with a community-level net isotope effect of 4.19 ± 0.29‰. We also observe significant deviation of our data from modelled and observed utilisation trends, and argue that this is driven primarily by water column nitrification and meltwater dilution of surface nitrate. This study is important because it provides a detailed description of the nutrient biogeochemistry underlying high primary productivity at the WAP, and shows that surface ocean nutrient inventories in the Antarctic sea ice zone can be affected by intense recycling in the water column, meltwater dilution and sea ice processes, in addition to utilisation in the upper ocean.

North Sea Storm Driving of Extreme Wave Heights

NASA Astrophysics Data System (ADS)

Bell, Ray; Gray, Suzanne; Jones, Oliver

2017-04-01

The relationship between storms and extreme ocean waves in the North sea is assessed using a long-period wave dataset and storms identified in the Interim ECMWF Re-Analysis (ERA-Interim). An ensemble sensitivity analysis is used to provide information on the spatial and temporal forcing from mean sea-level pressure and surface wind associated with extreme ocean wave height responses. Extreme ocean waves in the central North Sea arise due to either the winds in the cold conveyor belt (northerly-wind events) or winds in the warm conveyor belt (southerly-wind events) of extratropical cyclones. The largest wave heights are associated with northerly-wind events which tend to have stronger wind speeds and occur as the cold conveyor belt wraps rearwards round the cyclone to the cold side of the warm front. The northerly-wind events also provide a larger fetch to the central North Sea. Southerly-wind events are associated with the warm conveyor belts of intense extratropical storms developing in the right upper-tropospheric jet exit region. There is predictability in the extreme ocean wave events up to two days before the event associated with a strengthening of a high pressure system to the west (northerly-wind events) and south-west (southerly-wind events) of the British Isles. This acts to increase the pressure gradient over the British Isles and therefore drive stronger wind speeds in the central North sea.

The Effects of Ridge Axis Width on Mantle Melting at Mid-Ocean Ridges

NASA Astrophysics Data System (ADS)

Montesi, L.; Magni, V.; Gaina, C.

2017-12-01

Mantle upwelling in response to plate divergence produces melt at mid-ocean ridges. Melt starts when the solidus is crossed and stops when conductive cooling overcomes heat advection associated with the upwelling. Most mid-ocean ridge models assume that divergence takes place only in a narrow zone that defines the ridge axis, resulting in a single upwelling. However, more complex patterns of divergence are occasionally observed. The rift axis can be 20 km wide at ultraslow spreading center. Overlapping spreading center contain two parallel axes. Rifting in backarc basins is sometimes organized as a series of parallel spreading centers. Distributing plate divergence over several rifts reduces the intensity of upwelling and limits melting. Can this have a significant effect on the expected crustal thickness and on the mode of melt delivery at the seafloor? We address this question by modeling mantle flow and melting underneath two spreading centers separated by a rigid block. We adopt a non-linear rheology that includes dislocation creep, diffusion creep and yielding and include hydrothermal cooling by enhancing thermal conductivity where yielding takes place. The crustal thickness decreases if the rifts are separated by 30 km or more but only if the half spreading rate is between 1 and 2 cm/yr. At melting depth, a single upwelling remains the norm until the separation of the rifts exceeds a critical value ranging from 15 km in the fastest ridges to more than 50 km at ultraslow spreading centers. The stability of the central upwelling is due to hydrothermal cooling, which prevents hot mantle from reaching the surface at each spreading center. When hydrothermal cooling is suppressed, or the spreading centers are sufficiently separated, the rigid block becomes extremely cold and separates two distinct, highly asymmetric upwellings that may focus melt beyond the spreading center. In that case, melt delivery might drive further and further the divergence centers, whereas, when a single upwelling is retained, melt delivery would drive the spreading centers closer together. Thus, the system composed of two rifts is unstable and, if observed in nature, indicates either a transient geodynamic regime, like a recent change in spreading rates, or control structural or stress heterogeneities.

Simple models for the simulation of submarine melt for a Greenland glacial system model

NASA Astrophysics Data System (ADS)

Beckmann, Johanna; Perrette, Mahé; Ganopolski, Andrey

2018-01-01

Two hundred marine-terminating Greenland outlet glaciers deliver more than half of the annually accumulated ice into the ocean and have played an important role in the Greenland ice sheet mass loss observed since the mid-1990s. Submarine melt may play a crucial role in the mass balance and position of the grounding line of these outlet glaciers. As the ocean warms, it is expected that submarine melt will increase, potentially driving outlet glaciers retreat and contributing to sea level rise. Projections of the future contribution of outlet glaciers to sea level rise are hampered by the necessity to use models with extremely high resolution of the order of a few hundred meters. That requirement in not only demanded when modeling outlet glaciers as a stand alone model but also when coupling them with high-resolution 3-D ocean models. In addition, fjord bathymetry data are mostly missing or inaccurate (errors of several hundreds of meters), which questions the benefit of using computationally expensive 3-D models for future predictions. Here we propose an alternative approach built on the use of a computationally efficient simple model of submarine melt based on turbulent plume theory. We show that such a simple model is in reasonable agreement with several available modeling studies. We performed a suite of experiments to analyze sensitivity of these simple models to model parameters and climate characteristics. We found that the computationally cheap plume model demonstrates qualitatively similar behavior as 3-D general circulation models. To match results of the 3-D models in a quantitative manner, a scaling factor of the order of 1 is needed for the plume models. We applied this approach to model submarine melt for six representative Greenland glaciers and found that the application of a line plume can produce submarine melt compatible with observational data. Our results show that the line plume model is more appropriate than the cone plume model for simulating the average submarine melting of real glaciers in Greenland.

Recent tectonic activity on Pluto driven by phase changes in the ice shell

NASA Astrophysics Data System (ADS)

Hammond, Noah P.; Barr, Amy C.; Parmentier, Edgar M.

2016-07-01

The New Horizons spacecraft has found evidence for geologic activity on the surface of Pluto, including extensional tectonic deformation of its water ice bedrock see Moore et al. (2016). One mechanism that could drive extensional tectonic activity is global surface expansion due to the partial freezing of an ocean. We use updated physical properties for Pluto and simulate its thermal evolution to understand the survival of a possible subsurface ocean. For thermal conductivities of rock less than 3 W m-1 K-1, an ocean forms and at least partially freezes, leading to recent extensional stresses in the ice shell. In scenarios where the ocean freezes and the ice shell is thicker than 260 km, ice II forms and causes global volume contraction. Since there is no evidence for recent compressional tectonic features, we argue that ice II has not formed and that Pluto's ocean has likely survived to present day.

Abyssal Upwelling in Mid-Ocean Ridge Fracture Zones

NASA Astrophysics Data System (ADS)

Clément, Louis; Thurnherr, Andreas M.

2018-03-01

Turbulence in the abyssal ocean plays a fundamental role in the climate system by sustaining the deepest branch of the overturning circulation. Over the western flank of the Mid-Atlantic Ridge in the South Atlantic, previously observed bottom-intensified and tidally modulated mixing of abyssal waters appears to imply a counterintuitive densification of deep and bottom waters. Here we show that inside fracture zones, however, turbulence is elevated away from the seafloor because of intensified downward propagating near-inertial wave energy, which decays below a subinertial shear maximum. Ray-tracing simulations predict a decay of wave energy subsequent to wave-mean flow interactions. The hypothesized wave-mean flow interactions drive a deep flow toward lighter densities of up to 0.6 Sv over the mid-ocean ridge flank in the Brazil Basin, and the same process may also cause upwelling of abyssal waters in other ocean basins with mid-ocean ridges with fracture zones.

Impacts of atmospheric variability on a coupled upper-ocean/ecosystem model of the subarctic Northeast Pacific

NASA Astrophysics Data System (ADS)

Monahan, Adam Hugh; Denman, Kenneth L.

2004-06-01

The biologically-mediated flux of carbon from the upper ocean to below the permanent thermocline (the biological pump) is estimated to be ˜10 PgC/yr [, 2001], and plays an important role in the global carbon cycle. A detailed quantitative understanding of the dynamics of the biological pump is therefore important, particularly in terms of its potential sensitivity to climate change and its role in this change via feedback processes. Previous studies of coupled upper-ocean/planktonic ecosystem dynamics have considered models forced by observed atmospheric variability or by smooth annual and diurnal cycles. The second approach has the drawback that environmental variability is ubiquitous in the climate system, and may have a nontrivial impact on the (nonlinear) dynamics of the system, while the first approach is limited by the fact that observed time series are generally too short to obtain statistically robust characterizations of variability in the system. In the present study, an empirical stochastic model of high-frequency atmospheric variability (with a decorrelation timescale of less than a week) is estimated from long-term observations at Ocean Station Papa in the northeast subarctic Pacific. This empirical model, the second-order statistics of which resemble those of the observations to a good approximation, is used to produce very long (1000-year) realizations of atmospheric variability which are used to drive a coupled upper-ocean/ecosystem model. It is found that fluctuations in atmospheric forcing do not have an essential qualitative impact on most aspects of the dynamics of the ecosystem when primary production is limited by the availability of iron, although pronounced interannual variability in diatom abundance is simulated (even in the absence of episodic iron fertilization). In contrast, the impacts of atmospheric variability are considerably more significant when phytoplankton growth is limited in the summer by nitrogen availability, as observed closer to the North American coast. Furthermore, the high-frequency variability in atmospheric forcing is associated with regions in parameter space in which the system alternates between iron and nitrogen limitation on interannual to interdecadal timescales. Both the mean and variability of export production are found to be significantly larger in the nitrogen-limited regime than in the iron-limited regime.

Indian Ocean warming during 1958-2004 simulated by a climate system model and its mechanism

NASA Astrophysics Data System (ADS)

Dong, Lu; Zhou, Tianjun; Wu, Bo

2014-01-01

The mechanism responsible for Indian Ocean Sea surface temperature (SST) basin-wide warming trend during 1958-2004 is studied based on both observational data analysis and numerical experiments with a climate system model FGOALS-gl. To quantitatively estimate the relative contributions of external forcing (anthropogenic and natural forcing) and internal variability, three sets of numerical experiments are conducted, viz. an all forcing run forced by both anthropogenic forcing (greenhouse gases and sulfate aerosols) and natural forcing (solar constant and volcanic aerosols), a natural forcing run driven by only natural forcing, and a pre-industrial control run. The model results are compared to the observations. The results show that the observed warming trend during 1958-2004 (0.5 K (47-year)-1) is largely attributed to the external forcing (more than 90 % of the total trend), while the residual is attributed to the internal variability. Model results indicate that the anthropogenic forcing accounts for approximately 98.8 % contribution of the external forcing trend. Heat budget analysis shows that the surface latent heat flux due to atmosphere and surface longwave radiation, which are mainly associated with anthropogenic forcing, are in favor of the basin-wide warming trend. The basin-wide warming is not spatially uniform, but with an equatorial IOD-like pattern in climate model. The atmospheric processes, oceanic processes and climatological latent heat flux together form an equatorial IOD-like warming pattern, and the oceanic process is the most important in forming the zonal dipole pattern. Both the anthropogenic forcing and natural forcing result in easterly wind anomalies over the equator, which reduce the wind speed, thereby lead to less evaporation and warmer SST in the equatorial western basin. Based on Bjerknes feedback, the easterly wind anomalies uplift the thermocline, which is unfavorable to SST warming in the eastern basin, and contribute to SST warming via deeper thermocline in the western basin. The easterly anomalies also drive westward anomalous equatorial currents, against the eastward climatology currents, which is in favor of the SST warming in the western basin via anomalous warm advection. Therefore, both the atmospheric and oceanic processes are in favor of the IOD-like warming pattern formation over the equator.

Estimating the Cross-Shelf Export of Riverine Materials: Part 1. General Relationships From an Idealized Numerical Model

NASA Astrophysics Data System (ADS)

Izett, Jonathan G.; Fennel, Katja

2018-02-01

Rivers deliver large amounts of terrestrially derived materials (such as nutrients, sediments, and pollutants) to the coastal ocean, but a global quantification of the fate of this delivery is lacking. Nutrients can accumulate on shelves, potentially driving high levels of primary production with negative consequences like hypoxia, or be exported across the shelf to the open ocean where impacts are minimized. Global biogeochemical models cannot resolve the relatively small-scale processes governing river plume dynamics and cross-shelf export; instead, river inputs are often parameterized assuming an "all or nothing" approach. Recently, Sharples et al. (2017), https://doi.org/10.1002/2016GB005483 proposed the SP number—a dimensionless number relating the estimated size of a plume as a function of latitude to the local shelf width—as a simple estimator of cross-shelf export. We extend their work, which is solely based on theoretical and empirical scaling arguments, and address some of its limitations using a numerical model of an idealized river plume. In a large number of simulations, we test whether the SP number can accurately describe export in unforced cases and with tidal and wind forcings imposed. Our numerical experiments confirm that the SP number can be used to estimate export and enable refinement of the quantitative relationships proposed by Sharples et al. We show that, in general, external forcing has only a weak influence compared to latitude and derive empirical relationships from the results of the numerical experiments that can be used to estimate riverine freshwater export to the open ocean.

A 7.5-Year Dataset of SSM/I-Derived Surface Turbulent Fluxes Over Global Oceans

NASA Technical Reports Server (NTRS)

Chou, Shu-Hsien; Shie, Chung-Lin; Atlas, Robert M.; Ardizzone, Joe; Nelkin, Eric; Einaudi, Franco (Technical Monitor)

2001-01-01

The surface turbulent fluxes of momentum, latent heat, and sensible heat over global oceans are essential to weather, climate and ocean problems. Wind stress is the major forcing for driving the oceanic circulation, while Evaporation is a key component of hydrological cycle and surface heat budget. We have produced a 7.5-year (July 1987-December 1994) dataset of daily, individual monthly-mean and climatological (1988-94) monthly-mean surface turbulent fluxes over the global oceans from measurements of the Special Sensor Microwave/Imager (SSM/I) on board the US Defense Meteorological Satellite Program F8, F10, and F11 satellites. It has a spatial resolution of 2.0x2.5 latitude-longitude. Daily turbulent fluxes are derived from daily data of SSM/I surface winds and specific humidity, National Centers for Environmental Prediction (NCEP) sea surface temperatures, and European Centre for Medium-Range Weather Forecasts (ECMWF) air-sea temperature differences, using a stability-dependent bulk scheme. The retrieved instantaneous surface air humidity (with a 25-km resolution) IS found to be generally accurate as compared to the collocated radiosonde observations over global oceans. The surface wind speed and specific humidity (latent heat flux) derived from the F10 SSM/I are found to be -encrally smaller (larger) than those retrieved from the F11 SSM/I. The F11 SSM/I appears to have slightly better retrieval accuracy for surface wind speed and humidity as compared to the F10 SSM/I. This difference may be due to the orbital drift of the F10 satellite. The daily wind stresses and latent heat fluxes retrieved from F10 and F11 SSM/Is show useful accuracy as verified against the research quality in si -neasurerrients (IMET buoy, RV Moana Wave, and RV Wecoma) in the western Pacific warm pool during the TOGA COARE Intensive observing period (November 1992-February 1993). The 1988-94 seasonal-mean turbulent fluxes and input variables derived from FS and F11 SSM/Is show reasonable patterns related to seasonal variations of atmospheric general circulation. This dataset of SSM/I-derived turbulent fluxes is useful for climate studies, forcing of ocean models, and validation of coupled ocean-atmosphere global models and can be accessed through the NASA/GSFC Distributed Active Archive Center.

The influence of Seychelles Dome on the large scale Tropical Variability

NASA Astrophysics Data System (ADS)

Manola, Iris; Selten, Frank; Hazeleger, Wilco

2013-04-01

The Seychelles Dome (SD) is the thermocline ridge just South of the equator in the Western Indian Ocean basin. It is characterized by strong atmospheric convection and a shallow thermocline and is associated with large intraseasonal convection and SST variability (Harrison and Vecchi 2001). The SD is influenced by surface and subsurface processes, such as air-sea fluxes, Ekman upwelling from wind stress curl, ocean dynamics (vertical mixing) and oceanic Rossby waves from southeastern Indian Ocean. The favoring season for a strong SD is the boreal winter, where the thermocline is most shallow. Then the southeasterly trade winds converge with the northwesterly monsoonal winds over the intertropical convergence zone and cause cyclonic wind stress curl that drives Ekman divergence and a ridging of the thermocline. It is found that the subseasonal and interranual variability of the SD is influenced by large scale events, such as the Indian Ocean Dipole (IOD), the ENSO and the Madden-Julian Oscillation (MJO) (Tozuka et al., 2010, Lloyd and Vecchi, 2010). The SD is enhanced by cooling events in the Western Indian Ocean and easterly winds that raise the thermocline and increase the upwelling. This can be associated with a strong Walker circulation, like negative IOD conditions or La Nina-like conditions. So far the studies focus on the origins of the SD variability, but the influence of the SD itself on regional or large scale climate is largely unknown. In this study we focus on the influence of the SD variations on the large scale tropical circulation. We analyze the covariance of the SD variations and the tropical circulation in a 200 year control imulation of the climate model EC-EARTH and perform idealized SST forced simulations to study the character of the atmospheric response and its relation to ENSO, IOD and MJO. References -Harrison, D. E. and G. A. Vecchi, 2001: January 1999 Indian Ocean cooling event. Geophys. Res. Lett., 28, 3717-3720. -Lloyd, I. D., and G. A. Vecchi, 2010: Submonthly Indian Ocean cooling events and their interaction with large-scale conditions. J. Climate, 23, 700-716. -Tozuka, T., T. Yokoi, and T. Yamagata, 2010: A modeling study of interannual variations of the Seychelles Dome. J. Geophys. Res., 115, C04005, doi:10.1029/2009JC005547.

Edge systems in the deep ocean

NASA Astrophysics Data System (ADS)

Coon, Andrew; Earp, Samuel L.

2010-04-01

DARPA has initiated a program to explore persistent presence in the deep ocean. The deep ocean is difficult to access and presents a hostile environment. Persistent operations in the deep ocean will require new technology for energy, communications and autonomous operations. Several fundamental characteristics of the deep ocean shape any potential system architecture. The deep sea presents acoustic sensing opportunities that may provide significantly enhanced sensing footprints relative to sensors deployed at traditional depths. Communication limitations drive solutions towards autonomous operation of the platforms and automation of data collection and processing. Access to the seabed presents an opportunity for fixed infrastructure with no important limitations on size and weight. Difficult access and persistence impose requirements for long-life energy sources and potentially energy harvesting. The ocean is immense, so there is a need to scale the system footprint for presence over tens of thousands and perhaps hundreds of thousands of square nautical miles. This paper focuses on the aspect of distributed sensing, and the engineering of networks of sensors to cover the required footprint.

Dispersal, environmental niches and oceanic-scale turnover in deep-sea bivalves

PubMed Central

McClain, Craig R.; Stegen, James C.; Hurlbert, Allen H.

2012-01-01

Patterns of beta-diversity or distance decay at oceanic scales are completely unknown for deep-sea communities. Even when appropriate data exist, methodological problems have made it difficult to discern the relative roles of environmental filtering and dispersal limitation for generating faunal turnover patterns. Here, we combine a spatially extensive dataset on deep-sea bivalves with a model incorporating ecological dynamics and shared evolutionary history to quantify the effects of environmental filtering and dispersal limitation. Both the model and empirical data are used to relate functional, taxonomic and phylogenetic similarity between communities to environmental and spatial distances separating them for 270 sites across the Atlantic Ocean. This study represents the first ocean-wide analysis examining distance decay as a function of a broad suite of explanatory variables. We find that both strong environmental filtering and dispersal limitation drive turnover in taxonomic, functional and phylogenetic composition in deep-sea bivalves, explaining 26 per cent, 34 per cent and 9 per cent of the variation, respectively. This contrasts with previous suggestions that dispersal is not limiting in broad-scale biogeographic and biodiversity patterning in marine systems. However, rates of decay in similarity with environmental distance were eightfold to 44-fold steeper than with spatial distance. Energy availability is the most influential environmental variable evaluated, accounting for 3.9 per cent, 9.4 per cent and 22.3 per cent of the variation in functional, phylogenetic and taxonomic similarity, respectively. Comparing empirical patterns with process-based theoretical predictions provided quantitative estimates of dispersal limitation and niche breadth, indicating that 95 per cent of deep-sea bivalve propagules will be able to persist in environments that deviate from their optimum by up to 2.1 g m−2 yr−1 and typically disperse 749 km from their natal site. PMID:22189399

Constraints on Late Paleozoic Ocean Response to Climate Change Based on Brachiopod δ11B and 87Sr/86Sr

NASA Astrophysics Data System (ADS)

Legett, S. A.; Rasbury, T.; Grossman, E. L.; Hemming, G.

2017-12-01

In order to understand the possible effects of climate change on present day oceans, it is important to determine how marine systems responded to climate change in the past. This study uses δ11B values from well-preserved Carboniferous and Permian brachiopods as well as models to examine chemical trends in seawater and how these relate to long- and short-term climate changes. Our results show that δ11B rises rapidly going into the Carboniferous from a low of 10‰ to a high of 17‰ and remains relatively stable through the Carboniferous, despite the initiation of glaciation in the Mid Carboniferous. At the Carboniferous-Permian boundary, δ11B declines into the Early Permian before reaching a low at the Sakmarian. This decline in δ11B is coincident with the decrease in 87Sr/86Sr through this interval, which corresponds to evidence for aridity going into the Permian. We hypothesize that a reduction in silicate weathering drives an increase in atmospheric pCO2 and a subsequent lowering of ocean pH going into the Permian. This is consistent with our interpretation of the Carboniferous-Permian boundary, as a major mechanism for controlling seawater boron isotope composition is the adsorption of borate on clays, removing isotopically light boron and thus leaving seawater boron isotopically heavy. Therefore, at lower pH seawater should become isotopically lighter as this mechanism for removal is reduced. These hypotheses are supported by our initial modeling results of the B and Sr isotopic budgets of the ocean during the Late Paleozoic.

How does ocean seasonality drive habitat preferences of highly mobile top predators? Part II: The eastern North-Atlantic

NASA Astrophysics Data System (ADS)

Lambert, C.; Pettex, E.; Dorémus, G.; Laran, S.; Stéphan, E.; Canneyt, O. Van; Ridoux, V.

2017-07-01

Marine ecosystems are characterised by strong heterogeneity and variability, both spatially and temporally. In particular, seasonal variations may lead to severe constraints for predators which have to cope with these variations, for example through migration to avoid unfavourable seasons, or adaptation to local modification of the ecosystem. In the Bay of Biscay and English Channel, ecosystem seasonality is well marked, especially over the shelf. Cetacean and seabird communities within the Bay of Biscay, Celtic Sea and English Channel were studied during aerial surveys conducted in winter 2011-2012 and summer 2012, following a strip-transect methodology deployed from the coast to oceanic waters. We explored seasonal variations of habitat preferences of four cetacean and six seabird groups through Generalised Additive Models, using physiographic variables and weekly- and monthly-averaged oceanographic predictors for both seasons. Our results provided the first overview at such a large scale of the variation of habitat preferences in response to the seasonality of the ocean by seabirds in that region, at such a large scale. Habitat models resulted in explained deviances from 13 to 55%. Predators answered the seasonality of their environment in different ways. Long-finned pilot whales and Risso's dolphins were the only studied group exhibiting no habitat variations between seasons, targeting the shelf break throughout the year. The other groups modulated their habitat preferences between seasons to optimise the compromise between the ocean seasonal variations and their own constraints: common and striped dolphins, bottlenose dolphins and harbour porpoises for cetaceans; northern gannets, auks, northern fulmars and kittiwakes for seabirds. For shearwaters, the seasonality had an extreme impact, inducing a complete absence from the region during the unfavourable season.

76 FR 27643 - Ocean Transportation Intermediary License; Reissuance

Federal Register 2010, 2011, 2012, 2013, 2014

2011-05-12

.... Trade Management Group, LLC dba ITM Logistics dba Patriot Lines, 611 Live Oak Drive, McLean, VA 22101. 022665N Pacific Glory March 31, 2011. USA, Inc., 5673 Old Dixie Hwy., Suite 102, Forest Park, GA 30297...

Seabird diversity hotspot linked to ocean productivity in the Canary Current Large Marine Ecosystem

PubMed Central

Attrill, Martin J.; Becker, Peter H.; Egevang, Carsten; Furness, Robert W.; Grémillet, David; Kopp, Matthias; Lescroël, Amélie; Matthiopoulos, Jason; Peter, Hans-Ulrich; Phillips, Richard A.

2016-01-01

Upwelling regions are highly productive habitats targeted by wide-ranging marine predators and industrial fisheries. In this study, we track the migratory movements of eight seabird species from across the Atlantic; quantify overlap with the Canary Current Large Marine Ecosystem (CCLME) and determine the habitat characteristics that drive this association. Our results indicate the CCLME is a biodiversity hotspot for migratory seabirds; all tracked species and more than 70% of individuals used this upwelling region. Relative species richness peaked in areas where sea surface temperature averaged between 15 and 20°C, and correlated positively with chlorophyll a, revealing the optimum conditions driving bottom-up trophic effects for seabirds. Marine vertebrates are not confined by international boundaries, making conservation challenging. However, by linking diversity to ocean productivity, our research reveals the significance of the CCLME for seabird populations from across the Atlantic, making it a priority for conservation action. PMID:27531154

Ocean thermal plant

NASA Technical Reports Server (NTRS)

Owens, L. J. (Inventor)

1978-01-01

A floating energy converter is described which uses large volumes of sea water to produce electrical power. In this plant, a fluid working medium is pumped to an evaporator where is is heated by a flow of warm surface sea water. The fluid in liquid form boils to a pressurized gas vapor which is routed to drive a turbine that, in turn, drives a generator for producing electricity. The gas vapor then enters a condenser immersed in cold sea water pumped from lower depths, condenses to its original liquid form, and then pumped to the evaporator to repeat the cycle. Modular components can be readily interchanged on the ocean thermal unit and inlet pipes for the sea water are provided with means for maintaining the pipes in alignment with the oncoming current. The modular construction allows for the testing of various components to provide a more rapid optimization of a standardized plant.

Seabird diversity hotspot linked to ocean productivity in the Canary Current Large Marine Ecosystem.

PubMed

Grecian, W James; Witt, Matthew J; Attrill, Martin J; Bearhop, Stuart; Becker, Peter H; Egevang, Carsten; Furness, Robert W; Godley, Brendan J; González-Solís, Jacob; Grémillet, David; Kopp, Matthias; Lescroël, Amélie; Matthiopoulos, Jason; Patrick, Samantha C; Peter, Hans-Ulrich; Phillips, Richard A; Stenhouse, Iain J; Votier, Stephen C

2016-08-01

Upwelling regions are highly productive habitats targeted by wide-ranging marine predators and industrial fisheries. In this study, we track the migratory movements of eight seabird species from across the Atlantic; quantify overlap with the Canary Current Large Marine Ecosystem (CCLME) and determine the habitat characteristics that drive this association. Our results indicate the CCLME is a biodiversity hotspot for migratory seabirds; all tracked species and more than 70% of individuals used this upwelling region. Relative species richness peaked in areas where sea surface temperature averaged between 15 and 20°C, and correlated positively with chlorophyll a, revealing the optimum conditions driving bottom-up trophic effects for seabirds. Marine vertebrates are not confined by international boundaries, making conservation challenging. However, by linking diversity to ocean productivity, our research reveals the significance of the CCLME for seabird populations from across the Atlantic, making it a priority for conservation action. © 2016 The Authors.

Ross Ice Shelf airstream driven by polar vortex cyclone

NASA Astrophysics Data System (ADS)

Schultz, Colin

2012-07-01

The powerful air and ocean currents that flow in and above the Southern Ocean, circling in the Southern Hemisphere's high latitudes, form a barrier to mixing between Antarctica and the rest of the planet. Particularly during the austral winter, strong westerly winds isolate the Antarctic continent from heat, energy, and mass exchange, bolstering the scale of the annual polar ozone depletion and driving the continent's record-breaking low temperatures. Pushing through this wall of high winds, the Ross Ice Shelf airstream (RAS) is responsible for a sizable amount of mass and energy exchange from the Antarctic inland areas to lower latitudes. Sitting due south of New Zealand, the roughly 470,000-square-kilometer Ross Ice Shelf is the continent's largest ice shelf and a hub of activity for Antarctic research. A highly variable lower atmospheric air current, RAS draws air from the inland Antarctic Plateau over the Ross Ice Shelf and past the Ross Sea. Drawing on modeled wind patterns for 2001-2005, Seefeldt and Cassano identify the primary drivers of RAS.

Geothermal heating in the Panama Basin and its impact on water mass transformation

NASA Astrophysics Data System (ADS)

Banyte, D.; Morales Maqueda, M. A.; Hobbs, R. W.; Megann, A.; Smeed, D.

2017-12-01

Geothermal heating is a driving force of abyssal water transformation. To quantify its impact at the basin scale, a hydrographic survey of the Panama Basin was carried out in 2014-2015 as part of the international project OSCAR (Oceanographic and Seismic Characterisation of heat dissipation and alteration by hydrothermal fluids at an Axial Ridge). The study shows that about half of the water entering the basin, which is connected to the Pacific Ocean only through the a narrow passage part of the Ecuador Trench, is converted to lighter water within just 200 km downstream of the passage. Of the resulting water, a staggering 90% is transformed by geothermal heating inside the basin, welling up into the ocean interior from a bottom boundary layer (BBL) that can be up to 1000 m thick. The geothermal forcing leaves an imprint in temperature-salinity properties hundreds of meters above the thick BBL. We present a conceptual model of the abyssal water transformation in the basin that incorporates these processes.

The Earth's Biosphere

NASA Technical Reports Server (NTRS)

2002-01-01

In the last five years, scientists have been able to monitor our changing planet in ways never before possible. The Sea-viewing Wide Field-of-View Sensor (SeaWiFS), aboard the OrbView-2 satellite, has given researchers an unprecedented view of the biological engine that drives life on Earth-the countless forms of plants that cover the land and fill the oceans. 'There is no question the Earth is changing. SeaWiFS has enabled us, for the first time, to monitor the biological consequences of that change-to see how the things we do, as well as natural variability, affect the Earth's ability to support life,' said Gene Carl Feldman, SeaWiFS project manager at NASA's Goddard Space Flight Center, Greenbelt, Md. SeaWiFS data, based on continuous daily global observations, have helped scientists make a more accurate assessment of the oceans' role in the global carbon cycle. The data provide a key parameter in a number of ecological and environmental studies as well as global climate-change modeling. The images of the Earth's changing land, ocean and atmosphere from SeaWiFS have documented many previously unrecognized phenomena. The image above shows the global biosphere from June 2002 measured by SeaWiFS. Data in the oceans is chlorophyll concentration, a measure of the amount of phytoplankton (microscopic plants) living in the ocean. On land SeaWiFS measures Normalized Difference Vegetation Index, an indication of the density of plant growth. For more information and images, read: SeaWiFS Sensor Marks Five Years Documenting Earth'S Dynamic Biosphere Image courtesy SeaWiFS project and copyright Orbimage.

The climate response of the Indo-Pacific warm pool to glacial sea level

NASA Astrophysics Data System (ADS)

Di Nezio, Pedro N.; Timmermann, Axel; Tierney, Jessica E.; Jin, Fei-Fei; Otto-Bliesner, Bette; Rosenbloom, Nan; Mapes, Brian; Neale, Rich; Ivanovic, Ruza F.; Montenegro, Alvaro

2016-06-01

Growing climate proxy evidence suggests that changes in sea level are important drivers of tropical climate change on glacial-interglacial timescales. These paleodata suggest that rainfall patterns over the Indo-Pacific warm pool (IPWP) are highly sensitive to the landmass configuration of the Maritime Continent and that lowered sea level contributed to large-scale drying during the Last Glacial Maximum (LGM, approximately 21,000 years B.P.). Using the Community Earth System Model Version 1.2 (CESM1), we investigate the mechanisms by which lowered sea level influenced the climate of the IPWP during the LGM. The CESM1 simulations show that, in agreement with previous hypotheses, changes in atmospheric circulation are initiated by the exposure of the Sunda and Sahul shelves. Ocean dynamical processes amplify the changes in atmospheric circulation by increasing the east-west sea surface temperature (SST) gradient along the equatorial Indian Ocean. The coupled mechanism driving this response is akin to the Bjerknes feedback and results in a large-scale climatic reorganization over the Indian Ocean with impacts extending from east Africa to the western tropical Pacific. Unlike exposure of the Sunda shelf, exposure of Sahul shelf and the associated changes in surface albedo play a key role because of the positive feedback. This mechanism could explain the pattern of dry (wet) eastern (western) Indian Ocean identified in climate proxies and LGM simulations. However, this response also requires a strengthened SST gradient along the equatorial Indian Ocean, a pattern that is not evident in marine paleoreconstructions. Strategies to resolve this issue are discussed.

The Possible Emergence of Life and Differentiation of a Shallow Biosphere on Irradiated Icy Worlds: The Example of Europa

NASA Astrophysics Data System (ADS)

Russell, Michael J.; Murray, Alison E.; Hand, Kevin P.

2017-12-01

Irradiated ice-covered ocean worlds with rocky mafic mantles may provide the conditions needed to drive the emergence and maintenance of life. Alkaline hydrothermal springs - relieving the geophysical, thermal, and chemical disequilibria between oceans and tidally stressed crusts - could generate inorganic barriers to the otherwise uncontrolled and kinetically disfavored oxidation of hydrothermal hydrogen and methane. Ionic gradients imposed across these inorganic barriers, comprising iron oxyhydroxides and sulfides, could drive the hydrogenation of carbon dioxide and the oxidation of methane through thermodynamically favorable metabolic pathways leading to early life-forms. In such chemostatic environments, fuels may eventually outweigh oxidants. Ice-covered oceans are primarily heated from below, creating convection that could transport putative microbial cells and cellular cooperatives upward to congregate beneath an ice shell, potentially giving rise to a highly focused shallow biosphere. It is here where electron acceptors, ultimately derived from the irradiated surface, could be delivered to such life-forms through exchange with the icy surface. Such zones would act as "electron disposal units" for the biosphere, and occupants might be transferred toward the surface by buoyant diapirs and even entrained into plumes.

Insights into Spatial Sensitivities of Ice Mass Response to Environmental Change from the SeaRISE Ice Sheet Modeling Project I: Antarctica

NASA Technical Reports Server (NTRS)

Nowicki, Sophie; Bindschadler, Robert A.; Abe-Ouchi, Ayako; Aschwanden, Andy; Bueler, Ed; Choi, Hyengu; Fastook, Jim; Granzow, Glen; Greve, Ralf; Gutowski, Gail;

Diagnosing oceanic nutrient deficiency

PubMed Central

2016-01-01

The supply of a range of nutrient elements to surface waters is an important driver of oceanic production and the subsequent linked cycling of the nutrients and carbon. Relative deficiencies of different nutrients with respect to biological requirements, within both surface and internal water masses, can be both a key indicator and driver of the potential for these nutrients to become limiting for the production of new organic material in the upper ocean. The availability of high-quality, full-depth and global-scale datasets on the concentrations of a wide range of both macro- and micro-nutrients produced through the international GEOTRACES programme provides the potential for estimation of multi-element deficiencies at unprecedented scales. Resultant coherent large-scale patterns in diagnosed deficiency can be linked to the interacting physical–chemical–biological processes which drive upper ocean nutrient biogeochemistry. Calculations of ranked deficiencies across multiple elements further highlight important remaining uncertainties in the stoichiometric plasticity of nutrient ratios within oceanic microbial systems and caveats with regards to linkages to upper ocean nutrient limitation. This article is part of the themed issue ‘Biological and climatic impacts of ocean trace element chemistry’. PMID:29035255

Diagnosing oceanic nutrient deficiency

NASA Astrophysics Data System (ADS)

Moore, C. Mark

2016-11-01

The supply of a range of nutrient elements to surface waters is an important driver of oceanic production and the subsequent linked cycling of the nutrients and carbon. Relative deficiencies of different nutrients with respect to biological requirements, within both surface and internal water masses, can be both a key indicator and driver of the potential for these nutrients to become limiting for the production of new organic material in the upper ocean. The availability of high-quality, full-depth and global-scale datasets on the concentrations of a wide range of both macro- and micro-nutrients produced through the international GEOTRACES programme provides the potential for estimation of multi-element deficiencies at unprecedented scales. Resultant coherent large-scale patterns in diagnosed deficiency can be linked to the interacting physical-chemical-biological processes which drive upper ocean nutrient biogeochemistry. Calculations of ranked deficiencies across multiple elements further highlight important remaining uncertainties in the stoichiometric plasticity of nutrient ratios within oceanic microbial systems and caveats with regards to linkages to upper ocean nutrient limitation. This article is part of the themed issue 'Biological and climatic impacts of ocean trace element chemistry'.

The Role of Soil Water and Land Feedbacks in Decadal Drought in Western North America

NASA Astrophysics Data System (ADS)

Langford, S.; Chikamoto, Y.; Noone, D. C.

2013-12-01

Western North America is susceptible to severe impacts of megadroughts, as evidenced by tree-core or lake sediment records. Future predictions suggest that this region will become more arid, with further consequences for water resources. Understanding the mechanisms of drought variability and persistence in western North America is critical for the eventual development of effective forecasting methods. The ocean is expected to be the main source of decadal memory in the system as the atmosphere varies on a much shorter timescale. The ocean's role in driving the low-frequency variability of the system is potentially predictable. However, low-frequency precipitation anomalies in western North America can occur in the absence of ocean feedbacks. Sea surface temperature anomalies in the north Pacific Ocean only account for around 20 per cent of the low-frequency winter precipitation in California in the CMIP5 historical runs. This is not sufficient to use the skill of global coupled models in predicting ocean conditions ahead of time to successfully forecast the possibility of long-term drought in western North America. Megadroughts therefore may be generated by unpredictable atmospheric noise, or persisted by other sources of low-frequency variability such as land processes and feedbacks. Snowpack in western North America is a crucial water resource for the surrounding communities, storing the winter precipitation for use later in the year. Likewise, soil moisture integrates the precipitation signal; the time scale depends on the depth and characteristics of the soil. Water storage and related variables are more predictable on longer timescales than precipitation, as measured by anomaly correlation for hindcasts compared to a 'perfect model' control run with CESM1.0.3. The importance of antecedent land conditions in persisting megadroughts in western North America is explored with ensemble simulations of CESM1.0.3, where the atmosphere is perturbed at the initiation and peak of a megadrought in the control run. Numerical experiments are used to test land-atmosphere feedbacks or memory sources, highlighting the sensitivity of megadrought initiation, persistence and termination to these antecedent conditions. The model results confirm the importance of land processes in projections of future decadal hydroclimate.

Late Quaternary Variability of Arctic Sea Ice: Insights From Biomarker Proxy Records and Model Simulations

NASA Astrophysics Data System (ADS)

Stein, R. H.; Fahl, K.; Gierz, P.; Niessen, F.; Lohmann, G.

2017-12-01

Over the last about four decades, coinciding with global warming and atmospheric CO2increase, the extent and thickness of Arctic sea ice has decreased dramatically, a decrease much more rapid than predicted by climate models. The driving forces of this change are still not fully understood. In this context, detailed paleoclimatic records going back beyond the timescale of direct observations, i.e., high-resolution Holocene records but also records representing more distant warm periods, may help to to distinguish and quantify more precisely the natural and anthropogenic greenhouse gas forcing of global climate change and related sea ice decrease. Here, we concentrate on sea ice biomarker records representing the penultimate glacial/last interglacial (MIS 6/MIS 5e) and the Holocene time intervals. Our proxy records are compared with climate model simulations using a coupled atmosphere-ocean general circulation model (AOGCM). Based on our data, polynya-type sea ice conditions probably occurred off the major ice sheets along the northern Barents and East Siberian continental margins during late MIS 6. Furthermore, we demonstrate that even during MIS 5e, i.e., a time interval when the high latitudes have been significantly warmer than today, sea ice existed in the central Arctic Ocean during summer, whereas sea ice was significantly reduced along the Barents Sea continental margin influenced by Atlantic Water inflow. Assuming a closed Bering Strait (no Pacific Water inflow) during early MIS 5, model simulations point to a significantly reduced sea ice cover in the central Arctic Ocean, a scenario that is however not supported by the proxy record and thus seems to be less realistic. Our Holocene biomarker proxy records from the Chukchi Sea indicate that main factors controlling the millennial Holocene variability in sea ice are probably changes in surface water and heat flow from the Pacific into the Arctic Ocean as well as the long-term decrease in summer insolation. Here, increased Pacific Water inflow (and heat flux) may have triggered the contemporaneous decrease in sea ice and maximum surface-water productivity during mid-Holocene times.

Early warning signals of Atlantic Meridional Overturning Circulation collapse in a fully coupled climate model

NASA Astrophysics Data System (ADS)

Boulton, Chris A.; Allison, Lesley C.; Lenton, Timothy M.

2014-12-01

The Atlantic Meridional Overturning Circulation (AMOC) exhibits two stable states in models of varying complexity. Shifts between alternative AMOC states are thought to have played a role in past abrupt climate changes, but the proximity of the climate system to a threshold for future AMOC collapse is unknown. Generic early warning signals of critical slowing down before AMOC collapse have been found in climate models of low and intermediate complexity. Here we show that early warning signals of AMOC collapse are present in a fully coupled atmosphere-ocean general circulation model, subject to a freshwater hosing experiment. The statistical significance of signals of increasing lag-1 autocorrelation and variance vary with latitude. They give up to 250 years warning before AMOC collapse, after ~550 years of monitoring. Future work is needed to clarify suggested dynamical mechanisms driving critical slowing down as the AMOC collapse is approached.

Early warning signals of Atlantic Meridional Overturning Circulation collapse in a fully coupled climate model

PubMed Central

Boulton, Chris A.; Allison, Lesley C.; Lenton, Timothy M.

2014-01-01

The Atlantic Meridional Overturning Circulation (AMOC) exhibits two stable states in models of varying complexity. Shifts between alternative AMOC states are thought to have played a role in past abrupt climate changes, but the proximity of the climate system to a threshold for future AMOC collapse is unknown. Generic early warning signals of critical slowing down before AMOC collapse have been found in climate models of low and intermediate complexity. Here we show that early warning signals of AMOC collapse are present in a fully coupled atmosphere-ocean general circulation model, subject to a freshwater hosing experiment. The statistical significance of signals of increasing lag-1 autocorrelation and variance vary with latitude. They give up to 250 years warning before AMOC collapse, after ~550 years of monitoring. Future work is needed to clarify suggested dynamical mechanisms driving critical slowing down as the AMOC collapse is approached. PMID:25482065

Early warning signals of Atlantic Meridional Overturning Circulation collapse in a fully coupled climate model.

PubMed

Boulton, Chris A; Allison, Lesley C; Lenton, Timothy M

2014-12-08

The Atlantic Meridional Overturning Circulation (AMOC) exhibits two stable states in models of varying complexity. Shifts between alternative AMOC states are thought to have played a role in past abrupt climate changes, but the proximity of the climate system to a threshold for future AMOC collapse is unknown. Generic early warning signals of critical slowing down before AMOC collapse have been found in climate models of low and intermediate complexity. Here we show that early warning signals of AMOC collapse are present in a fully coupled atmosphere-ocean general circulation model, subject to a freshwater hosing experiment. The statistical significance of signals of increasing lag-1 autocorrelation and variance vary with latitude. They give up to 250 years warning before AMOC collapse, after ~550 years of monitoring. Future work is needed to clarify suggested dynamical mechanisms driving critical slowing down as the AMOC collapse is approached.

Metal Sulfide Cluster Complexes and their Biogeochemical Importance in the Environment

NASA Astrophysics Data System (ADS)

Luther, George W.; Rickard, David T.

2005-10-01

Aqueous clusters of FeS, ZnS and CuS constitute a major fraction of the dissolved metal load in anoxic oceanic, sedimentary, freshwater and deep ocean vent environments. Their ubiquity explains how metals are transported in anoxic environmental systems. Thermodynamic and kinetic considerations show that they have high stability in oxic aqueous environments, and are also a significant fraction of the total metal load in oxic river waters. Molecular modeling indicates that the clusters are very similar to the basic structural elements of the first condensed phase forming from aqueous solutions in the Fe-S, Zn-S and Cu-S systems. The structure of the first condensed phase is determined by the structure of the cluster in solution. This provides an alternative explanation of Ostwald's Rule, where the most soluble, metastable phases form before the stable phases. For example, in the case of FeS, we showed that the first condensed phase is nanoparticulate, metastable mackinawite with a particle size of 2 nm consisting of about 150 FeS subunits, representing the end of a continuum between aqueous FeS clusters and condensed material. These metal sulfide clusters and nanoparticles are significant in biogeochemistry. Metal sulfide clusters reduce sulfide and metal toxicity and help drive ecology. FeS cluster formation drives vent ecology and AgS cluster formation detoxifies Ag in Daphnia magna neonates. We also note a new reaction between FeS and DNA and discuss the potential role of FeS clusters in denaturing DNA.

Mixing in seasonally stratified shelf seas: a shifting paradigm.

PubMed

Rippeth, Tom P

2005-12-15

Although continental shelf seas make up a relatively small fraction (ca 7%) of the world ocean's surface, they are thought to contribute significantly (20-50% of the total) to the open-ocean carbon dioxide storage through processes collectively known as the shelf sea pump. The global significance of these processes is determined by the vertical mixing, which drives the net CO(2) drawdown (which can occur only in stratified water). In this paper, we focus on identifying the processes that are responsible for mixing across the thermocline in seasonally stratified shelf seas. We present evidence that shear instability and internal wave breaking are largely responsible for thermocline mixing, a clear development from the first-order paradigm for the water column structure in continental shelf seas. The levels of dissipation observed are quantitatively consistent with the observed dissipation rates of the internal tide and near-inertial oscillations. It is perhaps because these processes make such a small contribution to the total energy dissipated in shelf seas that they are not well represented in current state-of-the-art numerical models of continental shelf seas. The results thus present a clear challenge to oceanographic models.

Improvements and Advances to the Cross-Calibrated Multi-Platform (CCMP) Ocean Vector Wind Analysis (V2.0 release)

NASA Astrophysics Data System (ADS)

Scott, J. P.; Wentz, F. J.; Hoffman, R. N.; Atlas, R. M.

2016-02-01

Ocean vector wind is a valuable climate data record (CDR) useful in observing and monitoring changes in climate and air-sea interactions. Ocean surface wind stress influences such processes as heat, moisture, and momentum fluxes between the atmosphere and ocean, driving ocean currents and forcing ocean circulation. The Cross-Calibrated Multi-Platform (CCMP) ocean vector wind analysis is a quarter-degree, six-hourly global ocean wind analysis product created using the variational analysis method (VAM) [Atlas et al., 1996; Hoffman et al., 2003]. The CCMP V1.1 wind product is a highly-esteemed, widely-used data set containing the longest gap-free record of satellite-based ocean vector wind data (July 1987 to June 2012). CCMP V1.1 was considered a "first-look" data set that used the most-timely, albeit preliminary, releases of satellite, in situ, and modeled ECMWF-Operational wind background fields. The authors have been working with the original producers of CCMP V1.1 to create an updated, improved, and consistently-reprocessed CCMP V2.0 ocean vector wind analysis data set. With Remote Sensing Systems (RSS) having recently updated all passive microwave satellite instrument calibrations and retrievals to the RSS Version-7 RTM standard, the reprocessing of the CCMP data set into a higher-quality CDR using inter-calibrated satellite inputs became feasible. In addition to the use of SSM/I, SSMIS, TRMM TMI, QuikSCAT, AMSRE, and WindSat instruments, AMSR2, GMI, and ASCAT have been also included in the CCMP V2.0 data set release, which has now been extended to the beginning of 2015. Additionally, the background field has been updated to use six-hourly, quarter-degree ERA-Interim wind vector inputs, and the quality-checks on the in situ data have been carefully reviewed and improved. The goal of the release of the CCMP V2.0 ocean wind vector analysis product is to serve as a merged ocean wind vector data set for climate studies. Diligent effort has been made by the authors to minimize systematic and spurious sources of error. The authors will present a complete discussion of upgrades made to the CCMP V2.0 data set, as well as present validation work that has been completed on the CCMP V2.0 wind analysis product.

Shaken, but not stirred: how vortical flow drives small-scale aggregations of gyrotactic phytoplankton

NASA Astrophysics Data System (ADS)

Barry, Michael; Durham, William; Climent, Eric; Stocker, Roman

2011-11-01

Coastal ocean observations reveal that motile phytoplankton form aggregations at the Kolmogorov scale (mm-cm), whereas non-motile cells do not. We propose a new mechanism for the formation of this small-scale patchiness based on the interplay of turbulence and gyrotactic motility. Counterintuitively, turbulence does not stir a plankton suspension to homogeneity but drives aggregations instead. Through controlled laboratory experiments we show that the alga Heterosigma akashiwo rapidly forms aggregations in a cavity-driven vortical flow that approximates Kolmogorov eddies. Gyrotactic motility is found to be the key ingredient for aggregation, as non-motile cells remain randomly distributed. Observations are in remarkable agreement with a 3D model, and the validity of this mechanism for generating patchiness has been extended to realistic turbulent flows using Direct Numerical Simulations. Because small-scale patchiness influences rates of predation, sexual reproduction, infection, and nutrient competition, this result indicates that gyrotactic motility can profoundly affect phytoplankton ecology.

Ice Stream Slowdown Will Drive Long-Term Thinning of the Ross Ice Shelf, With or Without Ocean Warming

NASA Astrophysics Data System (ADS)

Campbell, Adam J.; Hulbe, Christina L.; Lee, Choon-Ki

2018-01-01

As time series observations of Antarctic change proliferate, it is imperative that mathematical frameworks through which they are understood keep pace. Here we present a new method of interpreting remotely sensed change using spatial statistics and apply it to the specific case of thickness change on the Ross Ice Shelf. First, a numerical model of ice shelf flow is used together with empirical orthogonal function analysis to generate characteristic patterns of response to specific forcings. Because they are continuous and scalable in space and time, the patterns allow short duration observations to be placed in a longer time series context. Second, focusing only on changes that are statistically significant, the synthetic response surfaces are used to extract magnitude and timing of past events from the observational data. Slowdown of Kamb and Whillans Ice Streams is clearly detectable in remotely sensed thickness change. Moreover, those past events will continue to drive thinning into the future.

Local atmospheric forcing driving an unexpected California Current System response during the 2015-2016 El Niño

NASA Astrophysics Data System (ADS)

Frischknecht, Martin; Münnich, Matthias; Gruber, Nicolas

2017-01-01

The 2015-2016 El Niño contributed to large anomalies across the California Current System (CalCS), but these anomalies ceased unexpectedly in late 2015. Here we use a suite of three hindcast simulations with the Regional Oceanic Modeling System to assess the responsible mechanisms for this development. We find that the early buildup was primarily driven by the early onset of this event in the tropical Pacific, driving anomalies in the CalCS through the propagation of coastally trapped waves. In contrast, the abrupt end in the central CalCS was caused by the unusual onset of upwelling favorable winds in the fall of 2015, which offset the continuing remote forcing through the coastal waveguide. Nevertheless, low-nutrient anomalies persisted, causing anomalously low phytoplankton abundance in the upwelling season of 2016. This is a recurring pattern for all El Niño events over the last 37 years, suggesting predictive skill on seasonal timescales.

Flourishing ocean drives the end-Permian marine mass extinction

PubMed Central

Schobben, Martin; Stebbins, Alan; Ghaderi, Abbas; Strauss, Harald; Korn, Dieter; Korte, Christoph

2015-01-01

The end-Permian mass extinction, the most severe biotic crisis in the Phanerozoic, was accompanied by climate change and expansion of oceanic anoxic zones. The partitioning of sulfur among different exogenic reservoirs by biological and physical processes was of importance for this biodiversity crisis, but the exact role of bioessential sulfur in the mass extinction is still unclear. Here we show that globally increased production of organic matter affected the seawater sulfate sulfur and oxygen isotope signature that has been recorded in carbonate rock spanning the Permian−Triassic boundary. A bifurcating temporal trend is observed for the strata spanning the marine mass extinction with carbonate-associated sulfate sulfur and oxygen isotope excursions toward decreased and increased values, respectively. By coupling these results to a box model, we show that increased marine productivity and successive enhanced microbial sulfate reduction is the most likely scenario to explain these temporal trends. The new data demonstrate that worldwide expansion of euxinic and anoxic zones are symptoms of increased biological carbon recycling in the marine realm initiated by global warming. The spatial distribution of sulfidic water column conditions in shallow seafloor environments is dictated by the severity and geographic patterns of nutrient fluxes and serves as an adequate model to explain the scale of the marine biodiversity crisis. Our results provide evidence that the major biodiversity crises in Earth’s history do not necessarily implicate an ocean stripped of (most) life but rather the demise of certain eukaryotic organisms, leading to a decline in species richness. PMID:26240323

Pressure-gradient-driven nearshore circulation on a beach influenced by a large inlet-tidal shoal system

USGS Publications Warehouse

Shi, F.; Hanes, D.M.; Kirby, J.T.; Erikson, L.; Barnard, P.; Eshleman, J.

2011-01-01

The nearshore circulation induced by a focused pattern of surface gravity waves is studied at a beach adjacent to a major inlet with a large ebb tidal shoal. Using a coupled wave and wave-averaged nearshore circulation model, it is found that the nearshore circulation is significantly affected by the heterogeneous wave patterns caused by wave refraction over the ebb tidal shoal. The model is used to predict waves and currents during field experiments conducted near the mouth of San Francisco Bay and nearby Ocean Beach. The field measurements indicate strong spatial variations in current magnitude and direction and in wave height and direction along Ocean Beach and across the ebb tidal shoal. Numerical simulations suggest that wave refraction over the ebb tidal shoal causes wave focusing toward a narrow region at Ocean Beach. Due to the resulting spatial variation in nearshore wave height, wave-induced setup exhibits a strong alongshore nonuniformity, resulting in a dramatic change in the pressure field compared to a simulation with only tidal forcing. The analysis of momentum balances inside the surf zone shows that, under wave conditions with intensive wave focusing, the alongshore pressure gradient associated with alongshore nonuniform wave setup can be a dominant force driving circulation, inducing heterogeneous alongshore currents. Pressure-gradient- forced alongshore currents can exhibit flow reversals and flow convergence or divergence, in contrast to the uniform alongshore currents typically caused by tides or homogeneous waves.

Flourishing ocean drives the end-Permian marine mass extinction.

PubMed

Schobben, Martin; Stebbins, Alan; Ghaderi, Abbas; Strauss, Harald; Korn, Dieter; Korte, Christoph

2015-08-18

The end-Permian mass extinction, the most severe biotic crisis in the Phanerozoic, was accompanied by climate change and expansion of oceanic anoxic zones. The partitioning of sulfur among different exogenic reservoirs by biological and physical processes was of importance for this biodiversity crisis, but the exact role of bioessential sulfur in the mass extinction is still unclear. Here we show that globally increased production of organic matter affected the seawater sulfate sulfur and oxygen isotope signature that has been recorded in carbonate rock spanning the Permian-Triassic boundary. A bifurcating temporal trend is observed for the strata spanning the marine mass extinction with carbonate-associated sulfate sulfur and oxygen isotope excursions toward decreased and increased values, respectively. By coupling these results to a box model, we show that increased marine productivity and successive enhanced microbial sulfate reduction is the most likely scenario to explain these temporal trends. The new data demonstrate that worldwide expansion of euxinic and anoxic zones are symptoms of increased biological carbon recycling in the marine realm initiated by global warming. The spatial distribution of sulfidic water column conditions in shallow seafloor environments is dictated by the severity and geographic patterns of nutrient fluxes and serves as an adequate model to explain the scale of the marine biodiversity crisis. Our results provide evidence that the major biodiversity crises in Earth's history do not necessarily implicate an ocean stripped of (most) life but rather the demise of certain eukaryotic organisms, leading to a decline in species richness.

Subduction Drive of Plate Tectonics

NASA Astrophysics Data System (ADS)

Hamilton, W. B.

2003-12-01

Don Anderson emphasizes that plate tectonics is self-organizing and is driven by subduction, which rights the density inversion generated as oceanic lithosphere forms by cooling of asthenosphere from the top. The following synthesis owes much to many discussions with him. Hinge rollback is the key to kinematics, and, like the rest of actual plate behavior, is incompatible with bottom-up convection drive. Subduction hinges (which are under, not in front of, thin leading parts of arcs and overriding plates) roll back into subducting plates. The Pacific shrinks because bounding hinges roll back into it. Colliding arcs, increasing arc curvatures, back-arc spreading, and advance of small arcs into large plates also require rollback. Forearcs of overriding plates commonly bear basins which preclude shortening of thin plate fronts throughout periods recorded by basin strata (100 Ma for Cretaceous and Paleogene California). This requires subequal rates of advance and rollback, and control of both by subduction. Convergence rate is equal to rates of rollback and advance in many systems but is greater in others. Plate-related circulation probably is closed above 650 km. Despite the popularity of concepts of plumes from, and subduction into, lower mantle, there is no convincing evidence for, and much evidence against, penetration of the 650 in either direction. That barrier not only has a crossing-inhibiting negative Clapeyron slope but also is a compositional boundary between fractionated (not "primitive"), sluggish lower mantle and fertile, mobile upper mantle. Slabs sink more steeply than they dip. Slabs older than about 60 Ma when their subduction began sink to, and lie down on and depress, the 650-km discontinuity, and are overpassed, whereas younger slabs become neutrally buoyant in mid-upper mantle, into which they are mixed as they too are overpassed. Broadside-sinking old slabs push all upper mantle, from base of oceanic lithosphere down to the 650, back under shrinking oceans, forcing rapid Pacific spreading. Slabs suck forward overriding arcs and continental lithosphere, plus most subjacent mantle above the transition zone. Changes in sizes of oceans result primarily from transfer of oceanic lithosphere, so backarcs and expanding oceans spread only slowly. Lithosphere parked in, or displaced from, the transition zone, or mixed into mid-upper mantle, is ultimately recycled, and regional variations in age of that submerged lithosphere may account for some regional contrasts in MORB. Plate motions make no kinematic sense in either the "hotspot" reference frame (HS; the notion of fixed plumes is easily disproved) or the no-net-rotation frame (NNR) In both, for example, many hinges roll forward, impossible with gravity drive. Subduction-drive predictions are fulfilled, and paleomagnetic data are satisfied (as they are not in HS and NNR), in the alternative framework of propulsionless Antarctica fixed relative to sluggish lower mantle. Passive ridges migrate away from Antarctica on all sides, and migration of these and other ridges permits tapping fresh asthenosphere. (HS and NNR tend to fix ridges). Ridge migration and spreading rates accord with subduction drive. All trenches roll back when allowance is made for back-arc spreading and intracontinental deformation. Africa rotates slowly toward subduction systems in the NE, instead of moving rapidly E as in HS and NNR. Stable NW Eurasia is nearly stationary, instead of also moving rapidly, and S and E Eurasian deformation relates to subduction and rollback. The Americas move Pacificward at almost the full spreading rates of passive ridges behind them. Lithosphere has a slow net westward drift. Reference: W.B. Hamilton, An alternative Earth, GSA Today, in press.

Dynamics of the Indian-Ocean oxygen minimum zones

NASA Astrophysics Data System (ADS)

McCreary, Julian P.; Yu, Zuojun; Hood, Raleigh R.; Vinaychandran, P. N.; Furue, Ryo; Ishida, Akio; Richards, Kelvin J.

2013-05-01

In the Indian Ocean, mid-depth oxygen minimum zones (OMZs) occur in the Arabian Sea and the Bay of Bengal. The lower part of the Arabian-Sea OMZ (ASOMZ; below 400 m) intensifies northward across the basin; in contrast, its upper part (above 400 m) is located in the central/eastern basin, well east of the most productive regions along the western boundary. The Bay-of-Bengal OMZ (BBOMZ), although strong, is weaker than the ASOMZ. To investigate the processes that maintain the Indian-Ocean OMZs, we obtain a suite of solutions to a coupled biological/physical model. Its physical component is a variable-density, 61/2 >-layer model, in which each layer corresponds to a distinct dynamical regime or water-mass type. Its biological component has six compartments: nutrients, phytoplankton, zooplankton, two size classes of detritus, and oxygen. Because the model grid is non-eddy resolving (0.5°), the biological model also includes a parameterization of enhanced mixing based on the eddy kinetic energy derived from satellite observations. To explore further the impact of local processes on OMZs, we also obtain analytic solutions to a one-dimensional, simplified version of the biological model. Our control run is able to simulate basic features of the oxygen, nutrient, and phytoplankton fields throughout the Indian Ocean. The model OMZs result from a balance, or lack thereof, between a sink of oxygen by remineralization and subsurface oxygen sources due primarily to northward spreading of oxygenated water from the Southern Hemisphere, with a contribution from Persian-Gulf water in the northern Arabian Sea. The northward intensification of the lower ASOMZ results mostly from horizontal mixing since advection is weak in its depth range. The eastward shift of the upper ASOMZ is due primarily to enhanced advection and vertical eddy mixing in the western Arabian Sea, which spread oxygenated waters both horizontally and vertically. Advection carries small detritus from the western boundary into the central/eastern Arabian Sea, where it provides an additional source of remineralization that drives the ASOMZ to suboxic levels. The model BBOMZ is weaker than the ASOMZ because the Bay lacks a remote source of detritus from the western boundary. Although detritus has a prominent annual cycle, the model OMZs do not because there is not enough time for significant remineralization to occur.

76 FR 26255 - Marine Mammals; File No. 116-1691

Federal Register 2010, 2011, 2012, 2013, 2014

2011-05-06

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75 FR 70023 - Outer Continental Shelf (OCS), Western and Central Planning Areas, Gulf of Mexico (GOM) Oil and...

Federal Register 2010, 2011, 2012, 2013, 2014

2010-11-16

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Tropical Atlantic Impacts on the Decadal Climate Variability of the Tropical Ocean and Atmosphere.

NASA Astrophysics Data System (ADS)

Li, X.; Xie, S. P.; Gille, S. T.; Yoo, C.

2015-12-01

Previous studies revealed atmospheric bridges between the tropical Pacific, Atlantic, and Indian Ocean. In particular, several recent works indicate that the Atlantic sea surface temperature (SST) may contribute to the climate variability over the equatorial Pacific. Inspired by these studies, our work aims at investigating the impact of the tropical Atlantic on the entire tropical climate system, and uncovering the physical dynamics under these tropical teleconnections. We first performed a 'pacemaker' simulation by restoring the satellite era tropical Atlantic SST changes in a fully coupled model - the CESM1. Results reveal that the Atlantic warming heats the Indo-Western Pacific and cools the Eastern Pacific, enhances the Walker circulation and drives the subsurface Pacific to a La Niña mode, contributing to 60-70% of the above tropical changes in the past 30 years. The same pan-tropical teleconnections have been validated by the statistics of observations and 106 CMIP5 control simulations. We then used a hierarchy of atmospheric and oceanic models with different complexities, to single out the roles of atmospheric dynamics, atmosphere-ocean fluxes, and oceanic dynamics in these teleconnections. With these simulations we established a two-step mechanism as shown in the schematic figure: 1) Atlantic warming generates an atmospheric deep convection and induces easterly wind anomalies over the Indo-Western Pacific in the form of Kelvin waves, and westerly wind anomalies over the eastern equatorial Pacific as Rossby waves, in line with Gill's solution. This circulation changes warms the Indo-Western Pacific and cools the Eastern Pacific with the wind-evaporation-SST effect, forming a temperature gradient over the Indo-Pacific basins. 2) The temperature gradient further generates a secondary atmospheric deep convection, which reinforces the easterly wind anomalies over the equatorial Pacific and enhances the Walker circulation, triggering the Pacific to a La Niña mode with Bjerknes ocean dynamical feedback. This mechanism contributes to the understanding of the global decadal climate variability and predictability. In particular, Atlantic contributes to the Eastern Pacific cooling, which is considered as an important source of the recent global warming hiatus.

Oceans Melting Greenland (OMG): 2017 Observations and the First Look at Yearly Ocean/Ice Changes

NASA Astrophysics Data System (ADS)

Willis, J. K.; Rignot, E. J.; Fenty, I. G.; Khazendar, A.; Moller, D.; Tinto, K. J.; Morison, J.; Schodlok, M.; Thompson, A. F.; Fukumori, I.; Holland, D.; Forsberg, R.; Jakobsson, M.; Dinardo, S. J.

2017-12-01

Oceans Melting Greenland (OMG) is an airborne NASA Mission to investigate the role of the oceans in ice loss around the margins of the Greenland Ice Sheet. A five-year campaign, OMG will directly measure ocean warming and glacier retreat around all of Greenland. By relating these two, we will explore one of the most pressing open questions about how climate change drives sea level rise: How quickly are the warming oceans melting the Greenland Ice Sheet from the edges? This year, OMG collected its second set of both elevation maps of marine terminating glaciers and ocean temperature and salinity profiles around all of Greenland. This give us our first look at year-to-year changes in both ice volume at the margins, as well as the volume and extent of warm, salty Atlantic water present on the continental shelf. In addition, we will compare recent data in east Greenland waters with historical ocean observations that suggest a long-term warming trend there. Finally, we will briefly review the multi-beam sonar and airborne gravity campaigns—both of which were completed last year—and the dramatic improvement they had on bathymetry maps over the continental shelf around Greenland.

Global Biogeochemical Cycle of Si: Its Coupling to the Perturbed C-N-P cycles in Industrial Time

NASA Astrophysics Data System (ADS)

Lerman, A.; Li, D. D.; MacKenzie, F. T.

2010-12-01

The importance of silicon (Si) in global biogeochemical cycles is demonstrated by its abundance in the land and aquatic biomass, where Si/C is 0.02 in land plants and 0.15 in marine organisms. Estimates show that Si-bioproduction accounts for ~1.5% of terrestrial primary production, and ~4.5% in the coastal ocean. Human land-use activities have substantially changed regional patterns of vegetation distribution, soil conditions, and nutrient fluxes via runoff to the coastal ocean. Anthropogenic chemical fertilization of the land has caused a significant increase in fluvial nitrogen (N) and phosphorus (P) transport, whereas land-use and vegetation mass changes have caused variations in the riverine Si input, all eventually affecting the cycling of nutrients in the marine environment. We developed a global biogeochemical model of the Si cycle as coupled to the global C-N-P cycle model, TOTEM II (Terrestrial-Ocean-aTmosphere-Ecosystem-Model). In the model analysis from year 1700, taken as the start of the Anthropocene, to 2050, the bioproduction of Si on land and in the ocean is coupled to the bioproduction of C, perturbed by the atmospheric CO2 rise, land-use changes, and chemical fertilization. Also, temperature rise affects the Si cycling on land through bioproduction rates, terrestrial organic matter remineralization, and weathering, thereby affecting its delivery to the coastal zone. The results show that biouptake and subsequent release of Si on land strongly affect the Si river flux to the coastal ocean. During the 350-year period, Si river discharge has increased by ~10% until ~1940, decreasing since then to below its 1700 value and continuing to drop, under the current IPCC IS92 projections of CO2, temperature and other forcings. From 1700 to ~1950, land-use changes, associated with slash and burn of large areas of high-productivity land, caused a decrease of global land vegetation. Dissolution of Si in soil humus and weathering of silicate minerals are the main dissolved Si sources for rivers and groundwater. The decrease in Si uptake by land biomass made more Si available for river discharge, causing an increase in the Si river input until an increase in the land primary production reversed the process. Around 1950, the use of fertilizer on land, especially N and P, increased, driving the growth of coastal marine primary producers, including such Si organisms as diatoms, silicoflagellates, and sponge spicules, and thus causing a decrease of dissolved Si in the surface ocean. The percent decrease of coastal dissolved Si due to increased primary production is greater than that of surface open ocean due to the shorter residence time of Si in coastal water (~2.7 years) compared to that of surface open ocean (~10 years. The combination of the relatively small size and location of the coastal ocean at the junction of the land, atmosphere, and open ocean make it important to changes in water chemistry, in situ biological production, and sedimentary storage. Its buffer effect and fast response to perturbations are also shown in the results of this coupling study of the C-N-P-Si cycles.

Surface flux and ocean heat transport convergence contributions to seasonal and interannual variations of ocean heat content

NASA Astrophysics Data System (ADS)

Roberts, C. D.; Palmer, M. D.; Allan, R. P.; Desbruyeres, D. G.; Hyder, P.; Liu, C.; Smith, D.

2017-01-01

We present an observation-based heat budget analysis for seasonal and interannual variations of ocean heat content (H) in the mixed layer (Hmld) and full-depth ocean (Htot). Surface heat flux and ocean heat content estimates are combined using a novel Kalman smoother-based method. Regional contributions from ocean heat transport convergences are inferred as a residual and the dominant drivers of Hmld and Htot are quantified for seasonal and interannual time scales. We find that non-Ekman ocean heat transport processes dominate Hmld variations in the equatorial oceans and regions of strong ocean currents and substantial eddy activity. In these locations, surface temperature anomalies generated by ocean dynamics result in turbulent flux anomalies that drive the overlying atmosphere. In addition, we find large regions of the Atlantic and Pacific oceans where heat transports combine with local air-sea fluxes to generate mixed layer temperature anomalies. In all locations, except regions of deep convection and water mass transformation, interannual variations in Htot are dominated by the internal rearrangement of heat by ocean dynamics rather than the loss or addition of heat at the surface. Our analysis suggests that, even in extratropical latitudes, initialization of ocean dynamical processes could be an important source of skill for interannual predictability of Hmld and Htot. Furthermore, we expect variations in Htot (and thus thermosteric sea level) to be more predictable than near surface temperature anomalies due to the increased importance of ocean heat transport processes for full-depth heat budgets.

The Deep Meridional Overturning Circulation in the Indian Ocean Inferred from the GECCO Synthesis

NASA Astrophysics Data System (ADS)

Wang, W.; Koehl, A.; Stammer, D.

2012-04-01

The meridional overturning circulation in the Indian Ocean and its temporal variability in the GECCO ocean synthesis are being investigated. An analysis of the integrated circulation in different layers suggests that, on time average, 2.1 Sv enter the Indian Ocean in the bottom layer (>3200m) from the south and that 12.3 Sv leave the Indian Ocean in the upper and intermediate layers (<1500m), composed of the up-welled bottom layer inflow water, augmented by 9.6 Sv Indonesian Throughflow (ITF) water. The GECCO time-mean results differ significantly from those obtained by box inverse models, which, being based on individual hydrographic sections, are susceptible to aliasing. The GECCO solution has a large seasonal variation in its meridional overturning caused by the seasonal reversal of monsoon-related wind stress forcing. Associated seasonal variations of the deep meridional overturning range from -7 Sv in boreal winter to 3 Sv in summer. In addition, the upper and bottom transports across 34°S section show pronounced interannual variability with roughly biennial variations superimposed by strong anomalies during each La Niña phase as well as the ITF, which mainly affect the upper layer transports. On decadal and longer timescale, the meridional overturning variability as well as long-term trends differ before and after 1980. Notably, our analysis shows a rather stable trend for the period 1960-1979 and significant changes in the upper and bottom layer for the period 1980-2001. By means of a multivariate EOF analysis, the importance of Ekman dynamics as driving forces of the deep meridional overturning of the Indian Ocean on the interannual timescale is highlighted. The leading modes of the zonal and meridional wind stress favour a basin-wide meridional overturning mode via Ekman upwelling or downwelling mostly in the central and eastern Indian Ocean. Moreover, tropical zonal wind stress along the equator and alongshore wind stress off the Sumatra-Java coast contributes to evolution of IOD events.

Uncertainty and feasibility of dynamical downscaling for modeling tropical cyclones for storm surge simulation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yang, Zhaoqing; Taraphdar, Sourav; Wang, Taiping

This paper presents a modeling study conducted to evaluate the uncertainty of a regional model in simulating hurricane wind and pressure fields, and the feasibility of driving coastal storm surge simulation using an ensemble of region model outputs produced by 18 combinations of three convection schemes and six microphysics parameterizations, using Hurricane Katrina as a test case. Simulated wind and pressure fields were compared to observed H*Wind data for Hurricane Katrina and simulated storm surge was compared to observed high-water marks on the northern coast of the Gulf of Mexico. The ensemble modeling analysis demonstrated that the regional model wasmore » able to reproduce the characteristics of Hurricane Katrina with reasonable accuracy and can be used to drive the coastal ocean model for simulating coastal storm surge. Results indicated that the regional model is sensitive to both convection and microphysics parameterizations that simulate moist processes closely linked to the tropical cyclone dynamics that influence hurricane development and intensification. The Zhang and McFarlane (ZM) convection scheme and the Lim and Hong (WDM6) microphysics parameterization are the most skillful in simulating Hurricane Katrina maximum wind speed and central pressure, among the three convection and the six microphysics parameterizations. Error statistics of simulated maximum water levels were calculated for a baseline simulation with H*Wind forcing and the 18 ensemble simulations driven by the regional model outputs. The storm surge model produced the overall best results in simulating the maximum water levels using wind and pressure fields generated with the ZM convection scheme and the WDM6 microphysics parameterization.« less

Understanding ice sheet evolution to avoid massive sea level rise instead of experiencing it (Louis Agassiz Medal Lecture)

NASA Astrophysics Data System (ADS)

Rignot, Eric

2017-04-01

With unabated climate warming, massive sea level rise from the melting of ice sheets in Greenland and Antarctica looms at the horizon. This is unfortunately an experiment that we can afford to run only once. Satellite and airborne sensors have significantly helped reveal the magnitude of the mass balance of the ice sheets, where the changes take place, when they started, how they change with time and the nature of the physical processes controlling them. These observations have constrained the maturation of numerical modeling techniques for projecting changes in these ice sheets, including the coupling of ocean and ice sheet models, yet significant uncertainties remain to make these projections directly policy relevant and many challenges remain. I will review the state of balance of the ice sheets as we know it today and the fundamental processes that will drive fast ice sheet retreat and sea level change: ice-ocean interaction and iceberg calving. Ice-ocean interaction are dominated by the wind-forced intrusion of warm, salty, subsurface waters toward the ice sheet periphery to melt ice from below at rates orders of magnitude greater than at the surface. In Greenland, these rates are difficult to observe, but model simulations indicate rates of ice melt along vertical calving faces of meters per day, along with undercutting of the ice faces. Constraining the temperature of the ocean waters from high resolution models and observations, however, remains a significant challenge. I will describe the progress we have made in addressing one major issue which is the mapping of fjord bathymetry around Greenland to define the pathways for warm waters. In Antarctica, the rates of melt are measured from remote sensing data but averaged over long periods, so that we are dependent on in-situ observations to understand the interaction of ocean waters with ice within the sub-ice-shelf cavities. I will describe progress made in mapping the bathymetry of the ice shelves and how the results have impacted our understanding of these interactions. In terms of calving, there is a range of processes acting upon the glacier and ice shelf faces, proceeding from the surface and mostly from below, that are still not sufficiently well explored. I will discuss processes elucidated in Greenland (undercutting and rotation of ice blocks near floatation) and those that are not well known in Antarctica.

Europa's Habitability follows from Classical Dynamical Astronomy

NASA Astrophysics Data System (ADS)

Greenberg, R.

2001-11-01

Celestial mechanics is responsible for Jupiter's satellite Europa being a possible site for life in the solar system. The Laplace orbital resonance drives a substantial eccentricity. The mutually dependent relationship between orbital and rotational evolution and tidal processes in turn controls Europa's heating and stress. Heat is likely adequate to maintain a liquid water ocean, and to keep the surface ice thin. Tidal stress can explain characteristic and ubiquitous crack patterns (global and cycloidal), as well as drive observed shear displacement features. The characteristic ridge sets that cover tectonic terrain are likely built by tidal pumping of oceanic fluid and slush through cracks to the surface on a daily basis. Nearly half the surface is chaotic terrain, with morphology and other characteristics indicative of melt-through from below. Formation of both chaotic and tectonic terrains has continually resurfaced the satellite, while connecting the ocean to the surface and providing a variety of evolving environmental niches. As a result of tides, liquid water would daily bathe crustal cracks and surfaces with heat, transporting and mixing substances vertically. Thus a variety of habitable environments likely exist in the crust. Moreover, exposure of the ocean to the surface in the ways described here satisfies a necessary condition for life in the ocean as well, by providing access to oxidants which are available near the surface. These processes were recent, and thus most likely continue today. Longer term changes in environmental conditions in the crust, such as deactivation of individual cracks after thousands of years (due to non-synchronous rotation) and later crustal thawing (releasing any trapped organisms), provided drivers for adaptation, as well as opportunity for evolution. This work is supported by the NASA Planetary Geology and Geophysics Program and the NSF Life in Extreme Environments Program.

Oceanic Feedback to the Madden-Julian Oscillation: Mixing's Critical Role

NASA Astrophysics Data System (ADS)

Moum, J. N.; Pujiana, K.; Lien, R. C.; Smyth, W.

2016-02-01

The Madden-Julian Oscillation (MJO) in the Indian Ocean is a large-scale, propagating atmospheric disturbance in the equatorial latitude band characterized by reduced outgoing longwave radiation due to deep atmospheric convection, and at the surface by intense westerly wind bursts and a change in sign of the net surface heat flux. The ocean response is the formation of a near-surface Yoshida-Wyrtki Jet, which accelerates almost in balance with the surface wind stress. High shear at the Jet's base drives intense turbulence, both of which continue long after the atmospheric disturbance has passed (Moum et al., 2014). The sequence of MJOs observed in the 2011-2012 DYNAMO experiment suggested the possibility that the greater mixing due to more intense MJO wind bursts might reduce SST recovery rates following MJO passage, thus reducing upper ocean heat content available to drive future atmospheric convection. We have tested this with a statistical analysis of less-complete historical observations of MJOs documenting 50 previous events. Our analysis shows that 1) SST increases more rapidly following weak MJOs than strong MJOs, and within a 60-day window, 2) weak MJOs follow strong MJOs (and do not follow weak MJOs), 3) strong MJOs follow weak MJOs (and do not follow strong MJOs). We hypothesize that these results are the consequence of Jet-forced variations in subsurface mixing on SST recovery rates, thereby providing direct feedback to subsequent MJOs. Moum, J.N., S.P. de Szoeke, W.D. Smyth, J.B. Edson, H.L. DeWitt, A.J. Moulin, E.J. Thompson, C.J. Zappa, S.A. Rutledge, R.H. Johnson and C.W. Fairall, 2014. Air-sea interactions from westerly wind bursts during the November 2011 MJO in the Indian Ocean. Bull.Am.Met.Soc., 95, 1185-1199.

Atlantic Water transformation in the Nordic Seas and its influence on the export rate of the Overflow Waters

NASA Astrophysics Data System (ADS)

Garcia Quintana, Yarisbel; Wiesner, Pia; Hu, Xianmin; Myers, Paul

2017-04-01

The Nordic Seas (NS) are the main gateway between the Arctic and the Atlantic Oceans. The basin can be considered as the headwaters for the Meridional Overturning Circulation (MOC), for it is there that the Denmark Strait Overflow Water (DSOW) and the Iceland-Scotland Overflow Water (ISOW) acquire their properties. Their inflow into the North Atlantic Ocean occurs across the Greenland-Scotland ridge. Together with Labrador Sea Water, DSOW and ISOW are the main components of the North Atlantic Deep Water (NADW), which ventilates the lower limb of the Atlantic MOC. In spite recent studies exploring the export rate and later pathways of the overflows, the question about what drives them, remains. Here we explore the transformation of the Atlantic Water (AW) as it enters the NS through Denmark Strait, Iceland Faroe Ridge and Faroe Schotland Channel, as well as its pathways within the basin. To do so, we use an eddy-permitting ocean general circulation model run over the period 2002 to 2015. Two different approaches are used to track the AW transformation in the NS: the well-tested off-line Lagrangian tool ARIANE and on-line passive tracers. In both cases we use the same definition of AW to tag its inflow through the three entering sections. The overflows directly impact circulation and water properties in much of the deep Atlantic Ocean, thus a better understanding of the physical processes behind their variability is crucial a asset.

The Added Value to Global Model Projections of Climate Change by Dynamical Downscaling: A Case Study over the Continental U.S. using the GISS-ModelE2 and WRF Models

NASA Technical Reports Server (NTRS)

Racherla, P. N.; Shindell, D. T.; Faluvegi, G. S.

2012-01-01

Dynamical downscaling is being increasingly used for climate change studies, wherein the climates simulated by a coupled atmosphere-ocean general circulation model (AOGCM) for a historical and a future (projected) decade are used to drive a regional climate model (RCM) over a specific area. While previous studies have demonstrated that RCMs can add value to AOGCM-simulated climatologies over different world regions, it is unclear as to whether or not this translates to a better reproduction of the observed climate change therein. We address this issue over the continental U.S. using the GISS-ModelE2 and WRF models, a state-of-the-science AOGCM and RCM, respectively. As configured here, the RCM does not effect holistic improvement in the seasonally and regionally averaged surface air temperature or precipitation for the individual historical decades. Insofar as the climate change between the two decades is concerned, the RCM does improve upon the AOGCM when nudged in the domain proper, but only modestly so. Further, the analysis indicates that there is not a strong relationship between skill in capturing climatological means and skill in capturing climate change. Though additional research would be needed to demonstrate the robustness of this finding in AOGCM/RCM models generally, the evidence indicates that, for climate change studies, the most important factor is the skill of the driving global model itself, suggesting that highest priority should be given to improving the long-range climate skill of AOGCMs.

The role of declining summer sea ice extent in increasing Arctic winter precipitation

NASA Astrophysics Data System (ADS)

Hamman, J.; Roberts, A.; Cassano, J. J.; Nijssen, B.

2016-12-01

In the past three decades, the Arctic has experienced large declines in summer sea ice cover, permafrost extent, and spring snow cover, and increases in winter precipitation. This study explores the relationship between declining Arctic sea ice extent (IE) and winter precipitation (WP) across the Arctic land masses. The first part of this presentation presents the observed relationship between IE and WP. Using satellite estimates of IE and WP data based on a combination of in-situ observations and global reanalyses, we show that WP is negatively correlated with summer IE and that this relationship is strongest before the year 2000. After 2000, around the time IE minima began to decline most rapidly, the relationship between IE and WP degenerates. This indicates that other processes are driving changes in IE and WP. We hypothesize that positive anomalies in poleward moisture transport have historically driven anomalously low IE and high WP, and that since the significant decline in IE, moisture divergence from the central Arctic has been a larger contributor to WP over land. To better understand the physical mechanisms driving the observed changes in the Arctic climate system and the sensitivity of the Arctic climate system to declining sea ice, we have used the fully-coupled Regional Arctic System Model (RASM) to simulate two distinct sea ice climates. The first climate represents normal IE, while the second includes reduced summer IE. The second portion of this presentation analyzes these two RASM simulations, in conjunction with our observation-based analysis, to understand the coupled relationship between poleward moisture transport, IE, evaporation from the Arctic Ocean, and precipitation. We will present the RASM-simulated Arctic water budget and demonstrate the role of IE in driving WP anomalies. Finally, a spatial correlation analysis identifies characteristic patterns in IE, ocean evaporation, and polar cap convergence that contribute to anomalies in WP.

Sources of Intermodel Spread in the Lapse Rate and Water Vapor Feedbacks

DOE Office of Scientific and Technical Information (OSTI.GOV)

Po-Chedley, Stephen; Armour, Kyle C.; Bitz, Cecilia M.

Sources of intermodel differences in the global lapse rate (LR) and water vapor (WV) feedbacks are assessed using CO 2 forcing simulations from 28 general circulation models. Tropical surface warming leads to significant warming and moistening in the tropical and extratropical upper troposphere, signifying a nonlocal, tropical influence on extratropical radiation and feedbacks. Model spread in the locally defined LR and WV feedbacks is pronounced in the Southern Ocean because of large-scale ocean upwelling, which reduces surface warming and decouples the surface from the tropospheric response. The magnitude of local extratropical feedbacks across models and over time is well characterizedmore » using the ratio of tropical to extratropical surface warming. It is shown that model differences in locally defined LR and WV feedbacks, particularly over the southern extratropics, drive model variability in the global feedbacks. The cross-model correlation between the global LR and WV feedbacks therefore does not arise from their covariation in the tropics, but rather from the pattern of warming exerting a common control on extratropical feedback responses. Because local feedbacks over the Southern Hemisphere are an important contributor to the global feedback, the partitioning of surface warming between the tropics and the southern extratropics is a key determinant of the spread in the global LR and WV feedbacks. It is also shown that model Antarctic sea ice climatology influences sea ice area changes and southern extratropical surface warming. In conclusion, as a result, model discrepancies in climatological Antarctic sea ice area have a significant impact on the intermodel spread of the global LR and WV feedbacks.« less

Sources of Intermodel Spread in the Lapse Rate and Water Vapor Feedbacks

DOE PAGES

Po-Chedley, Stephen; Armour, Kyle C.; Bitz, Cecilia M.; ...

2018-03-23

Sources of intermodel differences in the global lapse rate (LR) and water vapor (WV) feedbacks are assessed using CO 2 forcing simulations from 28 general circulation models. Tropical surface warming leads to significant warming and moistening in the tropical and extratropical upper troposphere, signifying a nonlocal, tropical influence on extratropical radiation and feedbacks. Model spread in the locally defined LR and WV feedbacks is pronounced in the Southern Ocean because of large-scale ocean upwelling, which reduces surface warming and decouples the surface from the tropospheric response. The magnitude of local extratropical feedbacks across models and over time is well characterizedmore » using the ratio of tropical to extratropical surface warming. It is shown that model differences in locally defined LR and WV feedbacks, particularly over the southern extratropics, drive model variability in the global feedbacks. The cross-model correlation between the global LR and WV feedbacks therefore does not arise from their covariation in the tropics, but rather from the pattern of warming exerting a common control on extratropical feedback responses. Because local feedbacks over the Southern Hemisphere are an important contributor to the global feedback, the partitioning of surface warming between the tropics and the southern extratropics is a key determinant of the spread in the global LR and WV feedbacks. It is also shown that model Antarctic sea ice climatology influences sea ice area changes and southern extratropical surface warming. In conclusion, as a result, model discrepancies in climatological Antarctic sea ice area have a significant impact on the intermodel spread of the global LR and WV feedbacks.« less

What controls the variability of oxygen in the subpolar North Pacific?

NASA Astrophysics Data System (ADS)

Takano, Yohei

Dissolved oxygen is a widely observed chemical quantity in the oceans along with temperature and salinity. Changes in the dissolved oxygen have been observed over the world oceans. Observed oxygen in the Ocean Station Papa (OSP, 50°N, 145°W) in the Gulf of Alaska exhibits strong variability over interannual and decadal timescales, however, the mechanisms driving the observed variability are not yet fully understood. Furthermore, irregular sampling frequency and relatively short record length make it difficult to detect a low-frequency variability. Motivated by these observations, we investigate the mechanisms driving the low-frequency variability of oxygen in the subpolar North Pacific. The specific purposes of this study are (1) to evaluate the robustness of the observed low-frequency variability of dissolved oxygen and (2) to determine the mechanisms driving the observed variability using statistical data analysis and numerical simulations. To evaluate the robustness of the low-frequency variability, we conducted spectral analyses on the observed oxygen at OSP. To address the irregular sampling frequency we randomly sub-sampled the raw data to form 500 ensemble members with a regular time interval, and then performed spectral analyses. The resulting power spectrum of oxygen exhibits a robust low-frequency variability and a statistically significant spectral peak is identified at a timescale of 15--20 years. The wintertime oceanic barotropic streamfunction is significantly correlated with the observed oxygen anomaly at OSP with a north-south dipole structure over the North Pacific. We hypothesize that the observed low-frequency variability is primarily driven by the variability of large-scale ocean circulation in the North Pacific. To test this hypothesis, we simulate the three-dimensional distribution of oxygen anomaly between 1952 to 2001 using data-constrained circulation fields. The simulated oxygen anomaly shows an outstanding variability in the Gulf of Alaska, showing that this region is a hotspot of oxygen fluctuation. Anomalous advection acting on the climatological mean oxygen gradient is the source of oxygen variability in this simulation. Empirical Orthogonal Function (EOF) analyses of the simulated oxygen show that the two dominant modes of the oxygen anomaly explains more than 50% of oxygen variance over the North Pacific, that are closely related to the dominant modes of climate variability in the North Pacific (Pacific Decadal Oscillation and North Pacific Oscillation). Our results imply the important link between large-scale climate fluctuations, ocean circulation and biogeochemical tracers in the North Pacific.

Inter-annual variability of transparent exopolymer particles in the Arctic Ocean reveals high sensitivity to ecosystem changes.

PubMed

Engel, Anja; Piontek, Judith; Metfies, Katja; Endres, Sonja; Sprong, Pim; Peeken, Ilka; Gäbler-Schwarz, Steffi; Nöthig, Eva-Maria

2017-06-23

Transparent exopolymer particles (TEP) are a class of marine gel particles and important links between surface ocean biology and atmospheric processes. Derived from marine microorganisms, these particles can facilitate the biological pumping of carbon dioxide to the deep sea, or act as cloud condensation and ice nucleation particles in the atmosphere. Yet, environmental controls on TEP abundance in the ocean are poorly known. Here, we investigated some of these controls during the first multiyear time-series on TEP abundance for the Fram Strait, the Atlantic gateway to the Central Arctic Ocean. Data collected at the Long-Term Ecological Research observatory HAUSGARTEN during 2009 to 2014 indicate a strong biological control with highest abundance co-occurring with the prymnesiophyte Phaeocystis pouchetii. Higher occurrence of P. pouchetii in the Arctic Ocean has previously been related to northward advection of warmer Atlantic waters, which is expected to increase in the future. Our study highlights the role of plankton key species in driving climate relevant processes; thus, changes in plankton distribution need to be accounted for when estimating the ocean's biogeochemical response to global change.

Subduction hinge migration: The backwards component of plate tectonics

NASA Astrophysics Data System (ADS)

Stegman, D.; Freeman, J.; Schellart, W.; Moresi, L.; May, D.

2005-12-01

There are approximately 50 distinct segments of subduction zones in the world, of which 40% have oceanic lithosphere subducting under oceanic lithosphere. All of these ocean-ocean systems are currently experiencing hinge-rollback, with the exception of 2 (Mariana and Kermadec). In hinge-rollback, the surface trace of the suduction zone (trench) is moving in the opposite direction as the plate is moving (i.e. backwards). Coincidentally, the fastest moving plate boundary in the world is actually the Tonga trench at an estimated 17 cm/yr (backwards). Although this quite important process was recognized soon after the birth of plate tectonic theory (Elsasser, 1971), it has received only a limited amount of attention (Garfunkel, 1986; Kincaid and Olson, 1987) until recently. Laboratory models have shown that having a three dimensional experiment is essential in order to build a correct understanding of subduction. We have developed a numerical model with the neccessary 3-D geometry capable of investigating some fundamental questions of plate tectonics: How does hinge-rollback feedback into surface tectonics and mantle flow? What can we learn about the forces that drive plate tectonics by studying hinge-rollback? We will present a quantatitive analysis of the effect of the lateral width of subduction zones, the key aspect to understanding the nature of hinge-rollback. Additionally, particular emphasis has been put on gaining intuition through the use of movies (a 3-D rendering of the numerical models), illustrating the time evolution of slab interactions with the lower mantle as seen in such fields as velocity magnitude, strain rate, viscosity, as well as the toroidal and poloidal components of induced flow. This investigation is well-suited to developing direct comparisons with geological and geophysical observations such as geodetically determined hinge retreat rates, geochemical and petrological observations of arc volcanics and back-arc ridge basalts, timing and distribution of metamorphic core complexes in backarc basins under extension, paleostress observables such surface movements and block rotations, observations of seismic anistropy determined by shear wave splitting, and the emerging studies of regional tomographic models of seismic anistropy.

75 FR 16483 - Ocean Transportation Intermediary License Applicants

Federal Register 2010, 2011, 2012, 2013, 2014

2010-04-01

..., President Counterpoint Logistics LLC, 444 Donaldson Street, Highland Park, NJ 08904, Officer: Robby Lee..., Director (Qualifying Individual), S. Oxley, President Seapassion Logistics Inc., 12403 Slauson Avenue, Unit..., President United Sunfine Logistics, Inc., 20539 Walnut Drive, Suite F, Walnut, CA 91789, Officers: Andy Kung...

The OceanFlux Greenhouse Gases methodology for deriving a sea surface climatology of CO2 fugacity in support of air-sea gas flux studies

NASA Astrophysics Data System (ADS)

Goddijn-Murphy, L. M.; Woolf, D. K.; Land, P. E.; Shutler, J. D.; Donlon, C.

2015-07-01

Climatologies, or long-term averages, of essential climate variables are useful for evaluating models and providing a baseline for studying anomalies. The Surface Ocean CO2 Atlas (SOCAT) has made millions of global underway sea surface measurements of CO2 publicly available, all in a uniform format and presented as fugacity, fCO2. As fCO2 is highly sensitive to temperature, the measurements are only valid for the instantaneous sea surface temperature (SST) that is measured concurrently with the in-water CO2 measurement. To create a climatology of fCO2 data suitable for calculating air-sea CO2 fluxes, it is therefore desirable to calculate fCO2 valid for a more consistent and averaged SST. This paper presents the OceanFlux Greenhouse Gases methodology for creating such a climatology. We recomputed SOCAT's fCO2 values for their respective measurement month and year using monthly composite SST data on a 1° × 1° grid from satellite Earth observation and then extrapolated the resulting fCO2 values to reference year 2010. The data were then spatially interpolated onto a 1° × 1° grid of the global oceans to produce 12 monthly fCO2 distributions for 2010, including the prediction errors of fCO2 produced by the spatial interpolation technique. The partial pressure of CO2 (pCO2) is also provided for those who prefer to use pCO2. The CO2 concentration difference between ocean and atmosphere is the thermodynamic driving force of the air-sea CO2 flux, and hence the presented fCO2 distributions can be used in air-sea gas flux calculations together with climatologies of other climate variables.

How ocean acidification can benefit calcifiers.

PubMed

Connell, Sean D; Doubleday, Zoë A; Hamlyn, Sarah B; Foster, Nicole R; Harley, Christopher D G; Helmuth, Brian; Kelaher, Brendan P; Nagelkerken, Ivan; Sarà, Gianluca; Russell, Bayden D

2017-02-06

Reduction in seawater pH due to rising levels of anthropogenic carbon dioxide (CO 2 ) in the world's oceans is a major force set to shape the future of marine ecosystems and the ecological services they provide [1,2]. In particular, ocean acidification is predicted to have a detrimental effect on the physiology of calcifying organisms [3]. Yet, the indirect effects of ocean acidification on calcifying organisms, which may counter or exacerbate direct effects, is uncertain. Using volcanic CO 2 vents, we tested the indirect effects of ocean acidification on a calcifying herbivore (gastropod) within the natural complexity of an ecological system. Contrary to predictions, the abundance of this calcifier was greater at vent sites (with near-future CO 2 levels). Furthermore, translocation experiments demonstrated that ocean acidification did not drive increases in gastropod abundance directly, but indirectly as a function of increased habitat and food (algal biomass). We conclude that the effect of ocean acidification on algae (primary producers) can have a strong, indirect positive influence on the abundance of some calcifying herbivores, which can overwhelm any direct negative effects. This finding points to the need to understand ecological processes that buffer the negative effects of environmental change. Copyright © 2017 Elsevier Ltd. All rights reserved.

Decadal trends in Indian Ocean ambient sound.

PubMed

Miksis-Olds, Jennifer L; Bradley, David L; Niu, Xiaoyue Maggie

2013-11-01

The increase of ocean noise documented in the North Pacific has sparked concern on whether the observed increases are a global or regional phenomenon. This work provides evidence of low frequency sound increases in the Indian Ocean. A decade (2002-2012) of recordings made off the island of Diego Garcia, UK in the Indian Ocean was parsed into time series according to frequency band and sound level. Quarterly sound level comparisons between the first and last years were also performed. The combination of time series and temporal comparison analyses over multiple measurement parameters produced results beyond those obtainable from a single parameter analysis. The ocean sound floor has increased over the past decade in the Indian Ocean. Increases were most prominent in recordings made south of Diego Garcia in the 85-105 Hz band. The highest sound level trends differed between the two sides of the island; the highest sound levels decreased in the north and increased in the south. Rate, direction, and magnitude of changes among the multiple parameters supported interpretation of source functions driving the trends. The observed sound floor increases are consistent with concurrent increases in shipping, wind speed, wave height, and blue whale abundance in the Indian Ocean.

Discontinuous Galerkin modeling of the Columbia River's coupled estuary-plume dynamics

NASA Astrophysics Data System (ADS)

Vallaeys, Valentin; Kärnä, Tuomas; Delandmeter, Philippe; Lambrechts, Jonathan; Baptista, António M.; Deleersnijder, Eric; Hanert, Emmanuel

2018-04-01

The Columbia River (CR) estuary is characterized by high river discharge and strong tides that generate high velocity flows and sharp density gradients. Its dynamics strongly affects the coastal ocean circulation. Tidal straining in turn modulates the stratification in the estuary. Simulating the hydrodynamics of the CR estuary and plume therefore requires a multi-scale model as both shelf and estuarine circulations are coupled. Such a model has to keep numerical dissipation as low as possible in order to correctly represent the plume propagation and the salinity intrusion in the estuary. Here, we show that the 3D baroclinic discontinuous Galerkin finite element model SLIM 3D is able to reproduce the main features of the CR estuary-to-ocean continuum. We introduce new vertical discretization and mode splitting that allow us to model a region characterized by complex bathymetry and sharp density and velocity gradients. Our model takes into account the major forcings, i.e. tides, surface wind stress and river discharge, on a single multi-scale grid. The simulation period covers the end of spring-early summer of 2006, a period of high river flow and strong changes in the wind regime. SLIM 3D is validated with in-situ data on the shelf and at multiple locations in the estuary and compared with an operational implementation of SELFE. The model skill in the estuary and on the shelf indicate that SLIM 3D is able to reproduce the key processes driving the river plume dynamics, such as the occurrence of bidirectional plumes or reversals of the inner shelf coastal currents.

Equilibrium shoreline response of a high wave energy beach

USGS Publications Warehouse

Yates, M.L.; Guza, R.T.; O'Reilly, W. C.; Hansen, J.E.; Barnard, P.L.

2011-01-01

Four years of beach elevation surveys at Ocean Beach, San Francisco, California, are used to extend an existing equilibrium shoreline change model, previously calibrated with fine sand and moderate energy waves, to medium sand and higher-energy waves. The shoreline, characterized as the cross-shore location of the mean high water contour, varied seasonally by between 30 and 60 m, depending on the alongshore location. The equilibrium shoreline change model relates the rate of horizontal shoreline displacement to the hourly wave energy E and the wave energy disequilibrium, the difference between E and the equilibrium wave energy that would cause no change in the present shoreline location. Values for the model shoreline response coefficients are tuned to fit the observations in 500 m alongshore segments and averaged over segments where the model has good skill and the estimated effects of neglected alongshore sediment transport are relatively small. Using these representative response coefficients for 0.3 mm sand from Ocean Beach and driving the model with much lower-energy winter waves observed at San Onofre Beach (also 0.3 mm sand) in southern California, qualitatively reproduces the small seasonal shoreline fluctuations at San Onofre. This consistency suggests that the shoreline model response coefficients depend on grain size and may be constant, and thus transportable, between sites with similar grain size and different wave climates. The calibrated model response coefficients predict that for equal fluctuations in wave energy, changes in shoreline location on a medium-grained (0.3 mm) beach are much smaller than on a previously studied fine-grained (0.2 mm) beach. Copyright ?? 2011 by the American Geophysical Union.

The role of clouds in driving North Atlantic multi-decadal climate variability in observations and models

NASA Astrophysics Data System (ADS)

Clement, A. C.; Bellomo, K.; Murphy, L.

2013-12-01

Large scale warming and cooling periods of the North Atlantic is known as the Atlantic Multidecadal Oscillation (AMO). The pattern of warming and cooling in the North Atlantic Ocean over the 20th century that has a characteristic spatial structure with maximum warming in the mid-latitudes and subtropics. This has been most often attributed to changes in the strength of the Atlantic Meridional Overturning Circulation (AMOC), which in turn affects poleward heat transport. A recent modeling study by Booth et al. (2012), however, suggested that aerosols can explain both the spatial pattern and temporal history of Atlantic SST through indirect effects of aerosols on cloud cover; although this idea is controversial (Zhang et al., 2013). We have found observational evidence that changes in cloud amount can drive SST changes on multi-decadal timescale. We hypothesize that a positive local feedback between SST and cloud radiative effect amplifies SST and gives rise to the observed pattern of SST change. During cool North Atlantic periods, a southward shift of the ITCZ strengthens the trade winds in the tropical North Atlantic and increases low-level cloud cover, which acts to amplify the SST cooling in the North Atlantic. During warm periods in the North Atlantic, the opposite response occurs. We are testing whether the amplitude of this feedback is realistically simulated in the CMIP5 models, and whether inter-model differences in the amplitude of the feedback can explain differences in model simulations of Atlantic multi-decadal variability.

A Modelling Study of the Coastal Current in the Northwestern South China Sea: Response to Strong and Weak Southwest Monsoon

NASA Astrophysics Data System (ADS)

Ding, Y.; Yu, J.; Bao, X.; Yao, Z.

2016-02-01

The characteristics and dynamical mechanism of summer-time coastal current over the northwestern South China Sea (NSCS) shelf have been investigated based on a high resolution unstructured-grid finite volume community ocean model (FVCOM). Model-data comparison demonstrates that model well resolves the coastal dynamics over the NSCS shelf. The coastal current on the NSCS shelf is intensively influenced by monsoon and freshwater discharge of the Pearl River. Strong southwesterly wind drive the coastal current northeastward. However, under weak southwest monsoon, the coastal current west of Pearl River estuary (PRE) advects toward southwest, and splits into two parts when reaching east of the Qiongzhou Strait, with one branch entering the Gulf of Tonkin through the Qiongzhou Strait, transporting low salinity water into the Gulf of Tonkin, and the other part flows cyclonic and interacts with the northeastward current around southeast of Hainan Island, forming a cyclonic eddy east of the Qiongzhou Strait. A variety of model experiments focused on freshwater discharge, wind forcing, tidal rectification, and stratification are performed to study the physical mechanism of the southwestward coastal current which is usually against the summer wind. Process-oriented experiment results indicate that the southwest monsoon and freshwater discharge are important factors influencing the formation of southwestward coastal current during summer. Momentum balance analysis suggests that the along shelf barotropic pressure gradient due to the Pearl River discharge and wind forcing provides the main driving force for the southwestward coastal current.

Oceanic turbulence - Big bangs or continuous creation?

NASA Technical Reports Server (NTRS)

Caldwell, D. R.

1983-01-01

A hypothesis concerning the turbulence characteristics of 'microstructure' patches in the ocean is proposed in which a turbulence field is driven at the same time and scale at which it is observed. The driving energy is converted into turbulence kinetic energy in such a way that the observed overturning thickness scale is linearly related to the length scale. This hypothesis is contrasted with that of Gibson (1982), in which the 'patches' are produced by rare, powerful turbulence generators that have 'fossilized' prior to their observation. Careful attention is given to the sampling process and its assumptions.

The Possible Emergence of Life and Differentiation of a Shallow Biosphere on Irradiated Icy Worlds: The Example of Europa.

PubMed

Russell, Michael J; Murray, Alison E; Hand, Kevin P

2017-12-01

Irradiated ice-covered ocean worlds with rocky mafic mantles may provide the conditions needed to drive the emergence and maintenance of life. Alkaline hydrothermal springs-relieving the geophysical, thermal, and chemical disequilibria between oceans and tidally stressed crusts-could generate inorganic barriers to the otherwise uncontrolled and kinetically disfavored oxidation of hydrothermal hydrogen and methane. Ionic gradients imposed across these inorganic barriers, comprising iron oxyhydroxides and sulfides, could drive the hydrogenation of carbon dioxide and the oxidation of methane through thermodynamically favorable metabolic pathways leading to early life-forms. In such chemostatic environments, fuels may eventually outweigh oxidants. Ice-covered oceans are primarily heated from below, creating convection that could transport putative microbial cells and cellular cooperatives upward to congregate beneath an ice shell, potentially giving rise to a highly focused shallow biosphere. It is here where electron acceptors, ultimately derived from the irradiated surface, could be delivered to such life-forms through exchange with the icy surface. Such zones would act as "electron disposal units" for the biosphere, and occupants might be transferred toward the surface by buoyant diapirs and even entrained into plumes. Key Words: Biofilms-Europa-Extraterrestrial life-Hydrothermal systems. Astrobiology 17, 1265-1273.

The Possible Emergence of Life and Differentiation of a Shallow Biosphere on Irradiated Icy Worlds: The Example of Europa

PubMed Central

Murray, Alison E.; Hand, Kevin P.

2017-01-01

Abstract Irradiated ice-covered ocean worlds with rocky mafic mantles may provide the conditions needed to drive the emergence and maintenance of life. Alkaline hydrothermal springs—relieving the geophysical, thermal, and chemical disequilibria between oceans and tidally stressed crusts—could generate inorganic barriers to the otherwise uncontrolled and kinetically disfavored oxidation of hydrothermal hydrogen and methane. Ionic gradients imposed across these inorganic barriers, comprising iron oxyhydroxides and sulfides, could drive the hydrogenation of carbon dioxide and the oxidation of methane through thermodynamically favorable metabolic pathways leading to early life-forms. In such chemostatic environments, fuels may eventually outweigh oxidants. Ice-covered oceans are primarily heated from below, creating convection that could transport putative microbial cells and cellular cooperatives upward to congregate beneath an ice shell, potentially giving rise to a highly focused shallow biosphere. It is here where electron acceptors, ultimately derived from the irradiated surface, could be delivered to such life-forms through exchange with the icy surface. Such zones would act as “electron disposal units” for the biosphere, and occupants might be transferred toward the surface by buoyant diapirs and even entrained into plumes. Key Words: Biofilms—Europa—Extraterrestrial life—Hydrothermal systems. Astrobiology 17, 1265–1273. PMID:29016193

May common model biases reduce CMIP5's ability to simulate the recent Pacific La Niña-like cooling?

NASA Astrophysics Data System (ADS)

Luo, Jing-Jia; Wang, Gang; Dommenget, Dietmar

2018-02-01

Over the recent three decades sea surface temperate (SST) in the eastern equatorial Pacific has decreased, which helps reduce the rate of global warming. However, most CMIP5 model simulations with historical radiative forcing do not reproduce this Pacific La Niña-like cooling. Based on the assumption of "perfect" models, previous studies have suggested that errors in simulated internal climate variations and/or external radiative forcing may cause the discrepancy between the multi-model simulations and the observation. But the exact causes remain unclear. Recent studies have suggested that observed SST warming in the other two ocean basins in past decades and the thermostat mechanism in the Pacific in response to increased radiative forcing may also play an important role in driving this La Niña-like cooling. Here, we investigate an alternative hypothesis that common biases of current state-of-the-art climate models may deteriorate the models' ability and can also contribute to this multi-model simulations-observation discrepancy. Our results suggest that underestimated inter-basin warming contrast across the three tropical oceans, overestimated surface net heat flux and underestimated local SST-cloud negative feedback in the equatorial Pacific may favor an El Niño-like warming bias in the models. Effects of the three common model biases do not cancel one another and jointly explain 50% of the total variance of the discrepancies between the observation and individual models' ensemble mean simulations of the Pacific SST trend. Further efforts on reducing common model biases could help improve simulations of the externally forced climate trends and the multi-decadal climate fluctuations.

The deep meridional overturning circulation in the Indian Ocean inferred from the GECCO synthesis

NASA Astrophysics Data System (ADS)

Wang, Weiqiang; Köhl, Armin; Stammer, Detlef

2012-11-01

The deep time-varying meridional overturning circulation (MOC) in the Indian Ocean in the German “Estimating the Circulation and Climate of the Ocean” consortium efforts (GECCO) ocean synthesis is being investigated. An analysis of the integrated circulation suggests that, on time average, 2.1 Sv enter the Indian Ocean in the bottom layer (>3200 m) from the south and that 12.3 Sv leave the Indian Ocean in the upper and intermediate layers (<1500 m), composed of the up-welled bottom layer inflow water, augmented by 9.6 Sv Indonesian Throughflow (ITF) water. The GECCO time-mean results differ substantially from those obtained by inverse box models, which being based on individual hydrographic sections and due to the strong seasonal cycle are susceptible to aliasing. The GECCO solution shows a large seasonal variation in its deep MOC caused by the seasonal reversal of monsoon-related wind stress forcing. The associated seasonal variations of the deep MOC range from -7 Sv in boreal winter to 3 Sv in summer. In addition, the upper and bottom transports across the 34°S section show pronounced interannual variability with roughly biennial variations superimposed by strong anomalies during each La Niña phase as well as the ITF, which mainly affect the upper layer transports. On decadal and longer timescale, the meridional overturning variability as well as long-term trends differs before and after 1980. GECCO shows a stable trend for the period 1960-1979 and substantial changes in the upper and bottom layer for the period 1980-2001. By means of an extended EOF analysis, the importance of Ekman dynamics as driving forces of the deep MOC of the Indian Ocean on the interannual timescale is highlighted. The leading modes of the zonal and meridional wind stress favour a basin-wide meridional overturning mode via Ekman upwelling or downwelling mostly in the central and eastern Indian Ocean. Moreover, tropical zonal wind stress along the equator and alongshore wind stress off the Sumatra-Java coast contribute to the evolution of the Indian Ocean dipole (IOD) events.

Change in Dense Shelf Water and Adélie Land Bottom Water Precipitated by Iceberg Calving

NASA Astrophysics Data System (ADS)

Snow, K.; Rintoul, S. R.; Sloyan, B. M.; Hogg, A. McC.

2018-03-01

Antarctic Bottom Water supplies the deep limb of the global overturning circulation and ventilates the abyssal ocean. Antarctic Bottom Water has warmed, freshened, and contracted in recent decades, but the causes remain poorly understood. We use unique multiyear observations from the continental shelf and deep ocean near the Mertz Polynya to examine the sensitivity of this bottom water formation region to changes on the continental shelf, including the calving of a large iceberg. Postcalving, the seasonal cycle of Dense Shelf Water (DSW) density almost halved in amplitude and the volume of DSW available for export reduced. In the deep ocean, the density and volume of Adélie Land Bottom Water decreased sharply after calving, while oxygen concentrations remained high, indicating continued ventilation by DSW. This natural experiment illustrates how local changes in forcing over the Antarctic continental shelf can drive large and rapid changes in the abyssal ocean.

Near-island biological hotspots in barren ocean basins.

PubMed

Gove, Jamison M; McManus, Margaret A; Neuheimer, Anna B; Polovina, Jeffrey J; Drazen, Jeffrey C; Smith, Craig R; Merrifield, Mark A; Friedlander, Alan M; Ehses, Julia S; Young, Charles W; Dillon, Amanda K; Williams, Gareth J

2016-02-16

Phytoplankton production drives marine ecosystem trophic-structure and global fisheries yields. Phytoplankton biomass is particularly influential near coral reef islands and atolls that span the oligotrophic tropical oceans. The paradoxical enhancement in phytoplankton near an island-reef ecosystem--Island Mass Effect (IME)--was first documented 60 years ago, yet much remains unknown about the prevalence and drivers of this ecologically important phenomenon. Here we provide the first basin-scale investigation of IME. We show that IME is a near-ubiquitous feature among a majority (91%) of coral reef ecosystems surveyed, creating near-island 'hotspots' of phytoplankton biomass throughout the upper water column. Variations in IME strength are governed by geomorphic type (atoll vs island), bathymetric slope, reef area and local human impacts (for example, human-derived nutrient input). These ocean oases increase nearshore phytoplankton biomass by up to 86% over oceanic conditions, providing basal energetic resources to higher trophic levels that support subsistence-based human populations.

Zonally asymmetric response of the Southern Ocean mixed-layer depth to the Southern Annular Mode

NASA Astrophysics Data System (ADS)

Sallée, J. B.; Speer, K. G.; Rintoul, S. R.

2010-04-01

Interactions between the atmosphere and ocean are mediated by the mixed layer at the ocean surface. The depth of this layer is determined by wind forcing and heating from the atmosphere. Variations in mixed-layer depth affect the rate of exchange between the atmosphere and deeper ocean, the capacity of the ocean to store heat and carbon and the availability of light and nutrients to support the growth of phytoplankton. However, the response of the Southern Ocean mixed layer to changes in the atmosphere is not well known. Here we analyse temperature and salinity data from Argo profiling floats to show that the Southern Annular Mode (SAM), the dominant mode of atmospheric variability in the Southern Hemisphere, leads to large-scale anomalies in mixed-layer depth that are zonally asymmetric. From a simple heat budget of the mixed layer we conclude that meridional winds associated with departures of the SAM from zonal symmetry cause anomalies in heat flux that can, in turn, explain the observed changes of mixed-layer depth and sea surface temperature. Our results suggest that changes in the SAM, including recent and projected trends attributed to human activity, drive variations in Southern Ocean mixed-layer depth, with consequences for air-sea exchange, ocean sequestration of heat and carbon, and biological productivity.

78 FR 37540 - Ocean Transportation Intermediary License Applicants

Federal Register 2010, 2011, 2012, 2013, 2014

2013-06-21

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Federal Register 2010, 2011, 2012, 2013, 2014

2013-10-24

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75 FR 12749 - Ocean Transportation Intermediary License Revocations

Federal Register 2010, 2011, 2012, 2013, 2014

2010-03-17

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Synoptic-to-planetary scale wind variability enhances phytoplankton biomass at ocean fronts

NASA Astrophysics Data System (ADS)

Whitt, D. B.; Taylor, J. R.; Lévy, M.

2017-06-01

In nutrient-limited conditions, phytoplankton growth at fronts is enhanced by winds, which drive upward nutrient fluxes via enhanced turbulent mixing and upwelling. Hence, depth-integrated phytoplankton biomass can be 10 times greater at isolated fronts. Using theory and two-dimensional simulations with a coupled physical-biogeochemical ocean model, this paper builds conceptual understanding of the physical processes driving upward nutrient fluxes at fronts forced by unsteady winds with timescales of 4-16 days. The largest vertical nutrient fluxes occur when the surface mixing layer penetrates the nutricline, which fuels phytoplankton in the mixed layer. At a front, mixed layer deepening depends on the magnitude and direction of the wind stress, cross-front variations in buoyancy and velocity at the surface, and potential vorticity at the base of the mixed layer, which itself depends on past wind events. Consequently, mixing layers are deeper and more intermittent in time at fronts than outside fronts. Moreover, mixing can decouple in time from the wind stress, even without other sources of physical variability. Wind-driven upwelling also enhances depth-integrated phytoplankton biomass at fronts; when the mixed layer remains shallower than the nutricline, this results in enhanced subsurface phytoplankton. Oscillatory along-front winds induce both oscillatory and mean upwelling. The mean effect of oscillatory vertical motion is to transiently increase subsurface phytoplankton over days to weeks, whereas slower mean upwelling sustains this increase over weeks to months. Taken together, these results emphasize that wind-driven phytoplankton growth is both spatially and temporally intermittent and depends on a diverse combination of physical processes.

Variability and Predictability of West African Droughts. A Review in the Role of Sea Surface Temperature Anomalies

NASA Technical Reports Server (NTRS)

Rodriguez-Fonseca, Belen; Mohino, Elsa; Mechoso, Carlos R.; Caminade, Cyril; Biasutti, Michela; Gaetani, Marco; Garcia-Serrano, J.; Vizy, Edward K.; Cook, Kerry; Xue, Yongkang;

The interaction of climate change and methane hydrates

USGS Publications Warehouse

Ruppel, Carolyn D.; Kessler, John D.

2017-01-01

Gas hydrate, a frozen, naturally-occurring, and highly-concentrated form of methane, sequesters significant carbon in the global system and is stable only over a range of low-temperature and moderate-pressure conditions. Gas hydrate is widespread in the sediments of marine continental margins and permafrost areas, locations where ocean and atmospheric warming may perturb the hydrate stability field and lead to release of the sequestered methane into the overlying sediments and soils. Methane and methane-derived carbon that escape from sediments and soils and reach the atmosphere could exacerbate greenhouse warming. The synergy between warming climate and gas hydrate dissociation feeds a popular perception that global warming could drive catastrophic methane releases from the contemporary gas hydrate reservoir. Appropriate evaluation of the two sides of the climate-methane hydrate synergy requires assessing direct and indirect observational data related to gas hydrate dissociation phenomena and numerical models that track the interaction of gas hydrates/methane with the ocean and/or atmosphere. Methane hydrate is likely undergoing dissociation now on global upper continental slopes and on continental shelves that ring the Arctic Ocean. Many factors—the depth of the gas hydrates in sediments, strong sediment and water column sinks, and the inability of bubbles emitted at the seafloor to deliver methane to the sea-air interface in most cases—mitigate the impact of gas hydrate dissociation on atmospheric greenhouse gas concentrations though. There is no conclusive proof that hydrate-derived methane is reaching the atmosphere now, but more observational data and improved numerical models will better characterize the climate-hydrate synergy in the future.

The interaction of climate change and methane hydrates

NASA Astrophysics Data System (ADS)

Ruppel, Carolyn D.; Kessler, John D.

2017-03-01

Gas hydrate, a frozen, naturally-occurring, and highly-concentrated form of methane, sequesters significant carbon in the global system and is stable only over a range of low-temperature and moderate-pressure conditions. Gas hydrate is widespread in the sediments of marine continental margins and permafrost areas, locations where ocean and atmospheric warming may perturb the hydrate stability field and lead to release of the sequestered methane into the overlying sediments and soils. Methane and methane-derived carbon that escape from sediments and soils and reach the atmosphere could exacerbate greenhouse warming. The synergy between warming climate and gas hydrate dissociation feeds a popular perception that global warming could drive catastrophic methane releases from the contemporary gas hydrate reservoir. Appropriate evaluation of the two sides of the climate-methane hydrate synergy requires assessing direct and indirect observational data related to gas hydrate dissociation phenomena and numerical models that track the interaction of gas hydrates/methane with the ocean and/or atmosphere. Methane hydrate is likely undergoing dissociation now on global upper continental slopes and on continental shelves that ring the Arctic Ocean. Many factors—the depth of the gas hydrates in sediments, strong sediment and water column sinks, and the inability of bubbles emitted at the seafloor to deliver methane to the sea-air interface in most cases—mitigate the impact of gas hydrate dissociation on atmospheric greenhouse gas concentrations though. There is no conclusive proof that hydrate-derived methane is reaching the atmosphere now, but more observational data and improved numerical models will better characterize the climate-hydrate synergy in the future.

Changes in benthic ecosystems and ocean circulation in the Southeast Atlantic across Eocene Thermal Maximum 2

NASA Astrophysics Data System (ADS)

Jennions, S. M.; Thomas, E.; Schmidt, D. N.; Lunt, D.; Ridgwell, A.

2015-08-01

Eocene Thermal Maximum 2 (ETM2) occurred 1.8 Myr after the Paleocene-Eocene Thermal Maximum (PETM) and, like the PETM, was characterized by a negative carbon isotope excursion and warming. We combined benthic foraminiferal and sedimentological records for Southeast Atlantic Sites 1263 (1500 m paleodepth) and 1262 (3600 m paleodepth) to show that benthic foraminiferal diversity and accumulation rates declined more precipitously and severely at the shallower site during peak ETM2. As the sites are in close proximity, differences in surface productivity cannot have caused this differential effect. Instead, we infer that changes in ocean circulation across ETM2 may have produced more pronounced warming at intermediate depths (Site 1263). The effects of warming include increased metabolic rates, a decrease in effective food supply and increased deoxygenation, thus potentially explaining the more severe benthic impacts at Site 1263. In response, bioturbation may have decreased more at Site 1263 than at Site 1262, differentially affecting bulk carbonate records. We use a sediment-enabled Earth system model to test whether a reduction in bioturbation and/or the likely reduced carbonate saturation of more poorly ventilated waters can explain the more extreme excursion in bulk δ13C and sharper transition in wt % CaCO3 at Site 1263. We find that both enhanced acidification and reduced bioturbation during the ETM2 peak are needed to account for the observed features. Our combined ecological and modeling analysis illustrates the potential role of ocean circulation changes in amplifying local environmental changes and driving temporary, but drastic, loss of benthic biodiversity and abundance.

Variations of heat transport in the northwestern Pacific marginal seas inferred from high-resolution reanalysis

NASA Astrophysics Data System (ADS)

Seo, Gwang-Ho; Cho, Yang-Ki; Choi, Byoung-Ju

2014-02-01

High-resolution reanalysis of heat transport in the northwestern Pacific marginal seas was conducted for the period January 1980-December 2009 using ensemble Kalman filter. An ocean circulation model with a grid of 0.1 × 0.1° horizontal resolution and 20 vertical levels was used. Atmospheric forcing data from daily European Centre for Medium-Range Weather Forecasts were used in the ocean model. The assimilated data for the reanalysis were based on available observations of hydrographic profiles, including field surveys and Argo float and satellite-observed sea-surface temperature data. This study focused on mean and temporal variations in oceanic heat transport within the major straits among the marginal seas over 30 years. The mean heat transport in the Korea/Tsushima Strait and onshore transport across the shelf break in the East China Sea (ECS), Taiwan Strait, Tsugaru Strait, and Soya Strait were 182, 123, 82, 100, and 34 × 1012 W, respectively. The long-term trends in heat transport through the Korea/Tsushima Strait and Tsugaru Strait and onshore transport across the shelf break of the ECS were increasing, whereas the trend in heat transport through the Taiwan Strait was decreasing. There was little long-term change in heat transport in the Soya Strait. These long-term changes in heat transport through the Korea/Tsushima Strait, across the shelf of the ECS, and through the Taiwan Strait may be related to increased northeasterly wind stress in the ECS, which drives Ekman transport onto the shelf across the shelf break.

GOES-derived fog and low cloud indices for coastal north and central California ecological analyses

USGS Publications Warehouse

Torregrosa, Alicia; Cindy Combs,; Peters, Jeff

2015-01-01

Fog and low cloud cover (FLCC) changes the water, energy, and nutrient flux of coastal ecosystems. Easy-to-use FLCC data are needed to quantify the impacts of FLC on ecosystem dynamics during hot, dry Mediterranean climate summers. FLCC indices were generated from 26,000 hourly night and day FLCC maps derived from Geostationary Environmental Operational Satellite (GOES) data for June, July, August, and September, 1999- 2009 for coastal California, latitude 34.50°N, south of Monterey Bay, to latitude 41.95°N, north of Crescent City. Monthly FLCC average hours per day (h/d) range from < 2 to 18. Average FLCC over the ocean increases from north (9 h/d) to south (14 h/d) whereas FLCC over land is reversed. Over land, FLCC is highest where land juts into the prevailing NW winds and is lowest in the lee of major capes. FLCC advects furthest inland through low-lying NW ocean-facing valleys. At night hours of FLCC is higher more frequently on land than over the ocean. Interannual FLCC coefficient of variation shows long term geographic stability strongly associated with landform position. Contours delineating homogeneous zones of FLCC, derived from average decadal h/d FLCC, provide data to refine the commonly used term ‘fog belt.’ FLCC indices are available for download from the California Landscape Conservation Cooperative Climate Commons website. FLCC indices can be used to improve analyses of biogeographic and bioclimatic species distribution models, meteorological mechanisms driving FLCC patterns, ecohydrological investigations of evapotranspiration, solar energy feasibility studies, agricultural irrigation demand and viticultural ripening models.

Investigating the spring bloom initiation and net community production in the Subantarctic Southern Ocean using high-resolution in situ glider data

NASA Astrophysics Data System (ADS)

thomalla, sandy; Racault, Marie-Fanny; Swart, Sebastiaan; Monteiro, Pedro

2014-05-01

Phytoplankton bloom phenology has important consequences for marine ecosystems, fisheries and carbon export to the ocean interior. As such, it is important to examine the drivers of phytoplankton bloom initiation and their sensitivity to inter-annual climate variability and change. In this study we use ~6 months of in-situ high-resolution glider data to investigate the spring bloom initiation in the subantarctic zone (SAZ) of the Southern Ocean by implementing three different methods; a rate of change method, a threshold method and a cumulative sum method. The bloom initiation dates are critically compared to one another and the drivers of discrepancies assessed to inform on the sensitivities of different methods to processes driving the seasonal evolution of phytoplankton biomass in the subantarctic. The bloom initiation dates combined with in situ glider data of chlorophyll, light, and mixed layer depth allow us to resolve both Sverdrup's Critical Depth and Behrenfeld's Disturbance Recovery models through the water column and thus determine the seasonal evolution of net community production and respiration rates and the potential for carbon export. The outputs of the two different models are compared to one another in the context of their sensitivities to water column processes thereby refining their ability to address specific system scale questions. The novelty of this study is that gliders provide an unprecedented dataset to assess the seasonal cycle of phytoplankton biomass throughout the water column at high resolution, thus enhancing our understanding of net community production and export processes at submeso-space and sub-seasonal time scales.

Oceanic acidification affects marine carbon pump and triggers extended marine oxygen holes.

PubMed

Hofmann, Matthias; Schellnhuber, Hans-Joachim

2009-03-03

Rising atmospheric CO(2) levels will not only drive future global mean temperatures toward values unprecedented during the whole Quaternary but will also lead to massive acidification of sea water. This constitutes by itself an anthropogenic planetary-scale perturbation that could significantly modify oceanic biogeochemical fluxes and severely damage marine biota. As a step toward the quantification of such potential impacts, we present here a simulation-model-based assessment of the respective consequences of a business-as-usual fossil-fuel-burning scenario where a total of 4,075 Petagrams of carbon is released into the atmosphere during the current millennium. In our scenario, the atmospheric pCO(2) level peaks at approximately 1,750 microatm in the year 2200 while the sea-surface pH value drops by >0.7 units on global average, inhibiting the growth of marine calcifying organisms. The study focuses on quantifying 3 major concomitant effects. The first one is a significant (climate-stabilizing) negative feedback on rising pCO(2) levels as caused by the attenuation of biogenic calcification. The second one is related to the biological carbon pump. Because mineral ballast, notably CaCO(3), is found to play a dominant role in carrying organic matter through the water column, a reduction of its export fluxes weakens the strength of the biological carbon pump. There is, however, a third effect with severe consequences: Because organic matter is oxidized in shallow waters when mineral-ballast fluxes weaken, oxygen holes (hypoxic zones) start to expand considerably in the oceans in our model world--with potentially harmful impacts on a variety of marine ecosystems.

The interaction of climate change and methane hydrates

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ruppel, Carolyn D.; Kessler, John D.

Gas hydrate, a frozen, naturally-occurring, and highly-concentrated form of methane, sequesters significant carbon in the global system and is stable only over a range of low-temperature and moderate-pressure conditions. Gas hydrate is widespread in the sediments of marine continental margins and permafrost areas, locations where ocean and atmospheric warming may perturb the hydrate stability field and lead to release of the sequestered methane into the overlying sediments and soils. Methane and methane-derived carbon that escape from sediments and soils and reach the atmosphere could exacerbate greenhouse warming. The synergy between warming climate and gas hydrate dissociation feeds a popular perceptionmore » that global warming could drive catastrophic methane releases from the contemporary gas hydrate reservoir. Appropriate evaluation of the two sides of the climate-methane hydrate synergy requires assessing direct and indirect observational data related to gas hydrate dissociation phenomena and numerical models that track the interaction of gas hydrates/methane with the ocean and/or atmosphere. Methane hydrate is likely undergoing dissociation now on global upper continental slopes and on continental shelves that ring the Arctic Ocean. Many factors—the depth of the gas hydrates in sediments, strong sediment and water column sinks, and the inability of bubbles emitted at the seafloor to deliver methane to the sea-air interface in most cases—mitigate the impact of gas hydrate dissociation on atmospheric greenhouse gas concentrations though. There is no conclusive proof that hydrate-derived methane is reaching the atmosphere now, but more observational data and improved numerical models will better characterize the climate-hydrate synergy in the future.« less

The interaction of climate change and methane hydrates

DOE PAGES

Ruppel, Carolyn D.; Kessler, John D.

2016-12-14

Gas hydrate, a frozen, naturally-occurring, and highly-concentrated form of methane, sequesters significant carbon in the global system and is stable only over a range of low-temperature and moderate-pressure conditions. Gas hydrate is widespread in the sediments of marine continental margins and permafrost areas, locations where ocean and atmospheric warming may perturb the hydrate stability field and lead to release of the sequestered methane into the overlying sediments and soils. Methane and methane-derived carbon that escape from sediments and soils and reach the atmosphere could exacerbate greenhouse warming. The synergy between warming climate and gas hydrate dissociation feeds a popular perceptionmore » that global warming could drive catastrophic methane releases from the contemporary gas hydrate reservoir. Appropriate evaluation of the two sides of the climate-methane hydrate synergy requires assessing direct and indirect observational data related to gas hydrate dissociation phenomena and numerical models that track the interaction of gas hydrates/methane with the ocean and/or atmosphere. Methane hydrate is likely undergoing dissociation now on global upper continental slopes and on continental shelves that ring the Arctic Ocean. Many factors—the depth of the gas hydrates in sediments, strong sediment and water column sinks, and the inability of bubbles emitted at the seafloor to deliver methane to the sea-air interface in most cases—mitigate the impact of gas hydrate dissociation on atmospheric greenhouse gas concentrations though. There is no conclusive proof that hydrate-derived methane is reaching the atmosphere now, but more observational data and improved numerical models will better characterize the climate-hydrate synergy in the future.« less

Global Ocean Phytoplankton

NASA Technical Reports Server (NTRS)

Franz, B. A.; Behrenfeld, M. J.; Siegel, D. A.; Werdell, P. J.

2014-01-01

Marine phytoplankton are responsible for roughly half the net primary production (NPP) on Earth, fixing atmospheric CO2 into food that fuels global ocean ecosystems and drives the ocean's biogeochemical cycles. Phytoplankton growth is highly sensitive to variations in ocean physical properties, such as upper ocean stratification and light availability within this mixed layer. Satellite ocean color sensors, such as the Sea-viewing Wide Field-of-view Sensor (SeaWiFS; McClain 2009) and Moderate Resolution Imaging Spectroradiometer (MODIS; Esaias 1998), provide observations of sufficient frequency and geographic coverage to globally monitor physically-driven changes in phytoplankton distributions. In practice, ocean color sensors retrieve the spectral distribution of visible solar radiation reflected upward from beneath the ocean surface, which can then be related to changes in the photosynthetic phytoplankton pigment, chlorophyll- a (Chla; measured in mg m-3). Here, global Chla data for 2013 are evaluated within the context of the 16-year continuous record provided through the combined observations of SeaWiFS (1997-2010) and MODIS on Aqua (MODISA; 2002-present). Ocean color measurements from the recently launched Visible and Infrared Imaging Radiometer Suite (VIIRS; 2011-present) are also considered, but results suggest that the temporal calibration of the VIIRS sensor is not yet sufficiently stable for quantitative global change studies. All MODISA (version 2013.1), SeaWiFS (version 2010.0), and VIIRS (version 2013.1) data presented here were produced by NASA using consistent Chla algorithms.

Divergent plate motion drives rapid exhumation of (ultra)high pressure rocks

NASA Astrophysics Data System (ADS)

Liao, Jie; Malusà, Marco G.; Zhao, Liang; Baldwin, Suzanne L.; Fitzgerald, Paul G.; Gerya, Taras

2018-06-01

Exhumation of (ultra)high pressure [(U)HP] rocks by upper-plate divergent motion above an unbroken slab, first proposed in the Western Alps, has never been tested by numerical methods. We present 2D thermo-mechanical models incorporating subduction of a thinned continental margin beneath either a continental or oceanic upper plate, followed by upper-plate divergent motion away from the lower plate. Results demonstrate how divergent plate motion may trigger rapid exhumation of large volumes of (U)HP rocks directly to the Earth's surface, without the need for significant overburden removal by erosion. Model exhumation paths are fully consistent with natural examples for a wide range of upper-plate divergence rates. Exhumation rates are systematically higher than the divergent rate imposed to the upper plate, and the modeled size of exhumed (U)HP domes is invariant for different rates of upper-plate divergence. Major variations are instead predicted at depth for differing model scenarios, as larger amounts of divergent motion may allow mantle-wedge exhumation to shallow depth under the exhuming domes. The transient temperature increase, due to ascent of mantle-wedge material in the subduction channel, has a limited effect on exhumed continental (U)HP rocks already at the surface. We test two examples, the Cenozoic (U)HP terranes of the Western Alps (continental upper plate) and eastern Papua New Guinea (oceanic upper plate). The good fit between model predictions and the geologic record in these terranes encourages the application of these models globally to pre-Cenozoic (U)HP terranes where the geologic record of exhumation is only partly preserved.

Ice sheets play important role in climate change

NASA Astrophysics Data System (ADS)

Clark, Peter U.; MacAyeal, Douglas R.; Andrews, John T.; Bartlein, Patrick J.

Ice sheets once were viewed as passive elements in the climate system enslaved to orbitally generated variations in solar radiation. Today, modeling results and new geologic records suggest that ice sheets actively participated in late-Pleistocene climate change, amplifying or driving significant variability at millennial as well as orbital timescales. Although large changes in global ice volume were ultimately caused by orbital variations (the Milankovitch hypothesis), once in existence, the former ice sheets behaved dynamically and strongly influenced regional and perhaps even global climate by altering atmospheric and oceanic circulation and temperature.Experiments with General Circulation Models (GCMs) yielded the first inklings of ice sheets' climatic significance. Manabe and Broccoli [1985], for example, found that the topographic and albedo effects of ice sheets alone explain much of the Northern Hemisphere cooling identified in paleoclimatic records of the last glacial maximum (˜21 ka).

Pleistocene atmospheric CO2 change linked to Southern Ocean nutrient utilization

NASA Astrophysics Data System (ADS)

Ziegler, M.; Diz, P.; Hall, I. R.; Zahn, R.

2011-12-01

Biological uptake of CO2 by the ocean and its subsequent storage in the abyss is intimately linked with the global carbon cycle and constitutes a significant climatic force1. The Southern Ocean is a particularly important region because its wind-driven upwelling regime brings CO2 laden abyssal waters to the surface that exchange CO2 with the atmosphere. The Subantarctic Zone (SAZ) is a CO2 sink and also drives global primary productivity as unutilized nutrients, advected with surface waters from the south, are exported via Subantarctic Mode Water (SAMW) as preformed nutrients to the low latitudes where they fuel the biological pump in upwelling areas. Recent model estimates suggest that up to 40 ppm of the total 100 ppm atmospheric pCO2 reduction during the last ice age were driven by increased nutrient utilization in the SAZ and associated feedbacks on the deep ocean alkalinity. Micro-nutrient fertilization by iron (Fe), contained in the airborne dust flux to the SAZ, is considered to be the prime factor that stimulated this elevated photosynthetic activity thus enhancing nutrient utilization. We present a millennial-scale record of the vertical stable carbon isotope gradient between subsurface and deep water (Δδ13C) in the SAZ spanning the past 350,000 years. The Δδ13C gradient, derived from planktonic and benthic foraminifera, reflects the efficiency of biological pump and is highly correlated (rxy = -0.67 with 95% confidence interval [0.63; 0.71], n=874) with the record of dust flux preserved in Antarctic ice cores6. This strongly suggests that nutrient utilization in the SAZ was dynamically coupled to dust-induced Fe fertilization across both glacial-interglacial and faster millennial timescales. In concert with ventilation changes of the deep Southern Ocean this drove ocean-atmosphere CO2 exchange and, ultimately, atmospheric pCO2 variability during the late Pleistocene.

Climate at high obliquity

NASA Astrophysics Data System (ADS)

Marshall, J.; Ferreira, D.; O'Gorman, P. A.; Seager, S.

2011-12-01

One method of studying earth-like exoplanets is to view earth as an exoplanet and consider how its climate might change if, for example, its obliquity were ranged from 0 to 90 degrees. High values of obliquity challenge our understanding of climate dynamics because if obliquity exceeds 54 degrees, then polar latitudes receive more energy per unit area than do equatorial latitudes. Thus the pole will become warmer than the equator and we are led to consider a world in which the meridional temperature gradients, and associated prevailing zonal wind, have the opposite sign to the present earth. The problem becomes even richer when one considers the dynamics of an ocean, should one exist below. A central question for the ocean circulation is: what is the pattern of surface winds at high obliquities?, for it is the winds that drive the ocean currents and thermohaline circulation. How do atmospheric weather systems growing in the easterly sheared middle latitude jets determine the surface wind pattern? Should one expect middle latitude easterly winds? Finally, a key aspect with regard to habitability is to understand how the atmosphere and ocean of this high obliquity planet work cooperatively together to transport energy meridionally, mediating the warmth of the poles and the coldness of the equator. How extreme are seasonal temperature fluctuations? Should one expect to find ice around the equator? Possible answers to some of these questions have been sought by experimentation with a coupled atmosphere, ocean and sea-ice General Circulation Model of an earth-like aquaplanet: i.e. a planet like our own but on which there is only an ocean but no land. The coupled climate is studied across a range of obliquities (23.5, 54 and 90). We present some of the descriptive climatology of our solutions and how they shed light on the deeper questions of coupled climate dynamics that motivate them. We also review what they tell us about habitability on such planets.

Isolating the atmospheric circulation response to Arctic sea-ice loss in the coupled climate system

NASA Astrophysics Data System (ADS)

Kushner, Paul; Blackport, Russell

2017-04-01

In the coupled climate system, projected global warming drives extensive sea-ice loss, but sea-ice loss drives warming that amplifies and can be confounded with the global warming process. This makes it challenging to cleanly attribute the atmospheric circulation response to sea-ice loss within coupled earth-system model (ESM) simulations of greenhouse warming. In this study, many centuries of output from coupled ocean/atmosphere/land/sea-ice ESM simulations driven separately by sea-ice albedo reduction and by projected greenhouse-dominated radiative forcing are combined to cleanly isolate the hemispheric scale response of the circulation to sea-ice loss. To isolate the sea-ice loss signal, a pattern scaling approach is proposed in which the local multidecadal mean atmospheric response is assumed to be separately proportional to the total sea-ice loss and to the total low latitude ocean surface warming. The proposed approach estimates the response to Arctic sea-ice loss with low latitude ocean temperatures fixed and vice versa. The sea-ice response includes a high northern latitude easterly zonal wind response, an equatorward shift of the eddy driven jet, a weakening of the stratospheric polar vortex, an anticyclonic sea level pressure anomaly over coastal Eurasia, a cyclonic sea level pressure anomaly over the North Pacific, and increased wintertime precipitation over the west coast of North America. Many of these responses are opposed by the response to low-latitude surface warming with sea ice fixed. However, both sea-ice loss and low latitude surface warming act in concert to reduce storm track strength throughout the mid and high latitudes. The responses are similar in two related versions of the National Center for Atmospheric Research earth system models, apart from the stratospheric polar vortex response. Evidence is presented that internal variability can easily contaminate the estimates if not enough independent climate states are used to construct them. References: Blackport, R. and P. Kushner, 2017: Isolating the atmospheric circulation response to Arctic sea-ice loss in the coupled climate system. J. Climate, in press. Blackport, R. and P. Kushner, 2016: The Transient and Equilibrium Climate Response to Rapid Summertime Sea Ice Loss in CCSM4. J. Climate, 29, 401-417, doi: 10.1175/JCLI-D-15-0284.1.

Role of extratropical cyclones in the recently observed increase in poleward moisture transport into the Arctic Ocean

NASA Astrophysics Data System (ADS)

Villamil-Otero, Gian A.; Zhang, Jing; He, Juanxiong; Zhang, Xiangdong

2018-01-01

Poleward atmospheric moisture transport (AMT) into the Arctic Ocean can change atmospheric moisture or water vapor content and cause cloud formation and redistribution, which may change downward longwave radiation and, in turn, surface energy budgets, air temperatures, and sea-ice production and melt. In this study, we found a consistently enhanced poleward AMT across 60°N since 1959 based on the NCAR-NCEP reanalysis. Regional analysis demonstrates that the poleward AMT predominantly occurs over the North Atlantic and North Pacific regions, contributing about 57% and 32%, respectively, to the total transport. To improve our understanding of the driving force for this enhanced poleward AMT, we explored the role that extratropical cyclone activity may play. Climatologically, about 207 extratropical cyclones move across 60°N into the Arctic Ocean each year, among which about 66 (32% of the total) and 47 (23%) originate from the North Atlantic and North Pacific Ocean, respectively. When analyzing the linear trends of the time series constructed by using a 20-year running window, we found a positive correlation of 0.70 between poleward yearly AMT and the integrated cyclone activity index (measurement of cyclone intensity, number, and duration). This shows the consistent multidecadal changes between these two parameters and may suggest cyclone activity plays a driving role in the enhanced poleward AMT. Furthermore, a composite analysis indicates that intensification and poleward extension of the Icelandic low and accompanying strengthened cyclone activity play an important role in enhancing poleward AMT over the North Atlantic region.

Crystallization of a compositionally stratified basal magma ocean

NASA Astrophysics Data System (ADS)

Laneuville, Matthieu; Hernlund, John; Labrosse, Stéphane; Guttenberg, Nicholas

2018-03-01

Earth's ∼3.45 billion year old magnetic field is regenerated by dynamo action in its convecting liquid metal outer core. However, convection induces an isentropic thermal gradient which, coupled with a high core thermal conductivity, results in rapid conducted heat loss. In the absence of implausibly high radioactivity or alternate sources of motion to drive the geodynamo, the Earth's early core had to be significantly hotter than the melting point of the lower mantle. While the existence of a dense convecting basal magma ocean (BMO) has been proposed to account for high early core temperatures, the requisite physical and chemical properties for a BMO remain controversial. Here we relax the assumption of a well-mixed convecting BMO and instead consider a BMO that is initially gravitationally stratified owing to processes such as mixing between metals and silicates at high temperatures in the core-mantle boundary region during Earth's accretion. Using coupled models of crystallization and heat transfer through a stratified BMO, we show that very high temperatures could have been trapped inside the early core, sequestering enough heat energy to run an ancient geodynamo on cooling power alone.

Effect of fjord geometry on tidewater glacier stability

NASA Astrophysics Data System (ADS)

Åkesson, Henning; Nisancioglu, Kerim H.; Nick, Faezeh M.

2016-04-01

Many marine-terminating glaciers have thinned, accelerated and retreated during the last two decades, broadly consistent with warmer atmospheric and oceanic conditions. However, these patterns involve considerable spatial and temporal variability, with diverse glacier behavior within the same regions. Similarly, reconstructions of marine-terminating glaciers indicate highly asynchronous retreat histories. While it is well known that retrograde slopes can cause marine ice sheet instabilities, the effect of lateral drag and fjord width has received less attention. Here, we test the hypothesis that marine outlet glacier stability is largely controlled by fjord width, and to a less extent by regional climate forcing. We employ a dynamic flowline model on idealized glacier geometries (representative of different outlet glaciers) to investigate geometric controls on decadal and longer times scales. The model accounts for driving and resistive stresses of glacier flow as well as along-flow stress transfer. It has a physical treatment of iceberg calving and a time-adaptive grid allowing for continuous tracking of grounding-line migration. We apply changes in atmospheric and oceanic forcing and show how wide and narrow fjord sections foster glacier (in)stabilities. We also evaluate the effect of including a surface mass balance - elevation feedback in such a setting. Finally, the relevance of these results to past and future marine-terminating glacier stability is discussed.

Investigating the origin of vagrant dusky groupers, Epinephelus marginatus (Lowe, 1834), in coastal waters of Réunion Island.

PubMed

Reid, Kerry; Crochelet, Estelle; Bloomer, Paulette; Hoareau, Thierry B

2016-10-01

Due to their geographic isolation, biotas of oceanic islands are likely influenced by episodic long distance dispersal events, but such observations are scarce. In June 2012, fishermen from Réunion Island caught an unknown specimen of grouper, identified as dusky grouper Epinephelus marginatus (Lowe, 1834). This was highly unexpected considering the large distance of its closest verified occurrence (South Africa, ∼2500km). To identify the origin of this specimen and the mechanisms driving this potential long distance colonization, we combined genetic analyses and hydrodynamic connectivity modeling approaches. Molecular markers and samples from various locations across the distribution range resulted in the identification of three putative source populations. The Réunion specimen clustered genetically with South Africa. The estimated spawning period in relation to the connectivity modeling of larvae showed no possible direct connection between South Africa and Réunion. However, connectivity was predicted through intermediate stepping stone populations likely located around the southern tip of Madagascar, where the occurrence of the species has yet to be verified. The results further highlight the potential role of the cyclone Bingiza (February 2011) in the connection between Madagascar and Réunion. This shows that cyclones may be an important driver in long distance colonization of oceanic islands. Copyright © 2016 Elsevier Inc. All rights reserved.

The HEXACO Model of Personality and Risky Driving Behavior.

PubMed

Burtăverde, Vlad; Chraif, Mihaela; Aniţei, Mihai; Dumitru, Daniela

2017-04-01

This research tested the association between the HEXACO personality model and risky driving behavior as well as the predictive power of the HEXACO model in explaining risky driving behavior compared with the Big Five model. In Sample 1, 227 undergraduate students completed measures of the HEXACO personality model, the Big Five model, and driving aggression. In Sample 2, 244 community respondents completed measures of the HEXACO personality model, the Big Five model, and driving styles. Results showed that the Honesty-Humility factor is an important addition to personality models that aim to explain risky driving behavior as being related to all forms of driving aggression as well as to maladaptive and adaptive driving styles and having incremental validity in predicting verbally aggressive expression, risky driving, high-velocity driving, and careful driving. Moreover, compared with the Big Five model, the HEXACO model had better predictive power of aggressive driving.

Scientists and Educators: Joining Forces to Enhance Ocean Science Literacy

NASA Astrophysics Data System (ADS)

Keener-Chavis, P.

2004-12-01

The need for scientists to work with educators to enhance the general public's understanding of science has been addressed for years in reports like Science for All Americans (1990), NSF in a Changing World (1995), Turning to the Sea: America's Ocean Future (1999), Discovering the Earth's Final Frontier, A U.S. Strategy for Ocean Exploration (2000), and most recently, the U.S. Commission on Ocean Policy Report (2004). As reported in The National Science Foundation's Center for Ocean Science Education Excellence (COSEE) Workshop Report (2000), "The Ocean Sciences community did not answer (this) call, even though their discovery that the ocean was a more critical driving force in the natural environment than previously thought possessed great educational significance." It has been further acknowledged that "rapid and extensive improvement of science education is unlikely to occur until it becomes clear to scientists that they have an obligation to become involved in elementary- and secondary-level science (The Role of Scientists in the Professional Development of Science Teachers, National Research Council, 1996.) This presentation will focus on teachers' perceptions of how scientists conduct research, scientists' perceptions of how teachers should teach, and some misconceptions between the two groups. Criteria for high-quality professional development for teachers working with scientists will also be presented, along with a brief overview of the National Oceanic and Atmospheric Administration's Ocean Exploration program efforts to bring teachers and ocean scientists together to further ocean science literacy at the national level through recommendations put forth in the U.S. Commission on Ocean Policy Report (2004).

78 FR 27238 - Ocean Transportation Intermediary License Applicants

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2013-05-09

... President (QI), Charles H. Fischer III, President, Application Type: QI Change. CNC Worldwide, Inc. (NVO), 5343 W. Imperial Highway, Suite 300, Los Angeles, CA 90045, Officers: Eric Cheon, Secretary (QI), Henry...), 446 Cloverleaf Drive, Baldwin Park, CA 91706, Officers: Alexander C. Sahagun, President (QI), Julian L...

Globalization: Ecological consequences of global-scale connectivity in people, resources and information

USDA-ARS?s Scientific Manuscript database

Globalization is a phenomenon affecting all facets of the Earth System. Within the context of ecological systems, it is becoming increasingly apparent that global connectivity among terrestrial systems, the atmosphere, and oceans is driving many ecological dynamics at finer scales and pushing thresh...

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... Logistics (NVO & OFF), 249 W. Fernfield Drive, Monterey Park, CA 91754, Officer: Tony Chen, President/VP..., Cypress, CA 90630, Officers: Cindy J. Lee, Secretary/CFO, (Qualifying Individual), Kathlyn Park, CEO.... Nguyen, Secretary/CFO, Application Type: New NVO & OFF License. Atlas Logistics LLC (NVO & OFF), 2801 NW...

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Federal Register 2010, 2011, 2012, 2013, 2014

2011-04-06

...: New NVO. Landstar Global Logistics, Inc. (NVO & OFF), 13410 Sutton Park Drive South, Jacksonville, FL... at (202) 523-5843 or by e-mail at [email protected] . Agility Logistics Corp. (OFF), 240 Commerce, Irvine... Sachs, Partner/Logistics Manager (Qualifying Individual), Ali Ismailzada, Partner/CFO, Application Type...

78 FR 33841 - Ocean Transportation Intermediary License Revocations

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... Revoked: May 16, 2013. Reason: Voluntary Surrender of License. License No.: 015890NF. Name: OEC Freight Chicago, Inc. Address: 501 Frontier Way, Bensenville, IL 60106. Date Revoked: May 6, 2013. Reason...: 124 Garden Gate Drive, Ponte Vedra Beach, FL 32082. Date Revoked: May 15, 2013. Reason: Voluntary...

Stratigraphic Signatures of Forearc Basin Formation Mechanisms

NASA Astrophysics Data System (ADS)

Mannu, U.; Ueda, K.; Gerya, T.; Willett, S.; Strasser, M.

2014-12-01

Forearc basins are loci of active sedimentation above the landward portion of accretionary prisms. Although these basins typically remain separated from the frontal prism by a forearc high, their evolution has a significant impact on the structure and deformation of the entire wedge. Formation of forearc basins has been proposed as a consequence of changes in wedge stability due to an increase of slab dip in subduction zones. Another hypothesis attributes this to higher hinterland sedimentation, which causes the rear of the wedge to stabilize and eventually develop a forearc basin. Basin stratigraphic architecture, revealed by high-resolution reflection seismic data and borehole data allows interpretation of structural development of the accretionary prism and associated basins with the goal of determining the underlying driving mechanism(s) of basin formation. In this study we supplement data interpretation with thermo-mechanical numerical models including high-resolution isochronal surface tracking to visualize the developing stratigraphy of basins that develop in subduction zone and wedge dynamic models. We use a dynamic 2D thermo mechanical model incorporating surface processes, strain weakening and sediment subduction. The model is a modification of I2VIS model, which is based on conservative, fully staggered finite differences and a non-diffusive marker- in-cell technique capable of modelling mantle convection. In the model different driving mechanisms for basin formation can be explored. Stratigraphic simulations obtained by isochronal surface tracking are compared to reflection pattern and stratigraphy of seismic and borehole data, respectively. Initial results from a model roughly representing the Nankai Trough Subduction Zone offshore Japan are compared to available seismic and Integrated Ocean Drilling (IODP) data. A calibrated model predicting forearc basin stratigraphy will be used to discern the underlying process of basins formation and wedge dynamics.

Historical Climate Change Impacts on the Hydrological Processes of the Ponto-Caspian Basin

NASA Astrophysics Data System (ADS)

Koriche, Sifan A.; Singarayer, Joy S.; Coe, Michael T.; Nandini, Sri; Prange, Matthias; Cloke, Hannah; Lunt, Dan

2017-04-01

The Ponto-Caspian basin is one of the largest basins globally, composed of a closed basin (Caspian Sea) and open basins connecting to the global ocean (Black and Azov Sea). Over the historical time period (1850-present) Caspian Sea levels have varied between -25 and -29mbsl (Arpe et al., 2012), resulting in considerable changes to the area of the lake (currently 371,000 km2). Given projections of future climate change and the importance of the Caspian Sea for fisheries, agriculture, and industry, it is vital to understand how sea levels may vary in the future. Hydrological models can be used to assess the impacts of climate change on hydrological processes for future forecasts. However, it is critical to first evaluate such models using observational data for the present and recent past, and to understand the key hydrological processes driving past changes in sea level. In this study, the Terrestrial Hydrological Model (THMB) (Coe, 2000, 2002) is applied and evaluated to investigate the hydrological processes of the Ponto-Caspian basin for the historical period 1900 to 2000. The model has been forced using observational reanalysis datasets (ERA-Interim, ERA-20) and historical climate model data outputs (from CESM and HadCM3 models) to investigate the variability in the Caspian Sea level and the major river discharges. We examine the differences produced by driving the hydrological model with reanalysis data or climate models. We evaluate the model performance compared to observational discharge measurements and Caspian Sea level data. Secondly, we investigated the sensitivity of historical Caspian Sea level variations to different aspects of climate changes to examine the most important processes involved over this time period.

Three-dimensional shear wave velocity structure in the Atlantic upper mantle

NASA Astrophysics Data System (ADS)

James, Esther Kezia Candace

Oceanic lithosphere constitutes the upper boundary layer of the Earth's convecting mantle. Its structure and evolution provide a vital window on the dynamics of the mantle and important clues to how the motions of Earth's surface plates are coupled to convection in the mantle below. The three-dimensional shear-velocity structure of the upper mantle beneath the Atlantic Ocean is investigated to gain insight into processes that drive formation of oceanic lithosphere. Travel times are measured for approximately 10,000 fundamental-mode Rayleigh waves, in the period range 30-130 seconds, traversing the Atlantic basin. Paths with >30% of their length through continental upper mantle are excluded to maximize sensitivity to the oceanic upper mantle. The lateral distribution of Rayleigh wave phase velocity in the Atlantic upper mantle is explored with two approaches. One, phase velocity is allowed to vary only as a function of seafloor age. Two, a general two-dimensional parameterization is utilized in order to capture perturbations to age-dependent structure. Phase velocity shows a strong dependence on seafloor age, and removing age-dependent velocity from the 2-D maps highlights areas of anomalously low velocity, almost all of which are proximal to locations of hotspot volcanism. Depth-dependent variations in vertically-polarized shear velocity (Vsv) are determined with two sets of 3-D models: a layered model that requires constant VSV in each depth layer, and a splined model that allows VSV to vary continuously with depth. At shallow depths (˜75 km) the seismic structure shows the expected dependence on seafloor age. At greater depths (˜200 km) high-velocity lithosphere is found only beneath the oldest seafloor; velocity variations beneath younger seafloor may result from temperature or compositional variations within the asthenosphere. The age-dependent phase velocities are used to constrain temperature in the mantle and show that, in contrast to previous results for the Pacific, phase velocities for the Atlantic are not consistent with a half-space cooling model but are best explained by a plate-cooling model with thickness of 75 km and mantle temperature of 1400°C. Comparison with data such as basalt chemistry and seafloor elevation helps to separate thermal and compositional effects on shear velocity.

Oxygen in the Southern Ocean From Argo Floats: Determination of Processes Driving Air-Sea Fluxes

NASA Astrophysics Data System (ADS)

Bushinsky, Seth M.; Gray, Alison R.; Johnson, Kenneth S.; Sarmiento, Jorge L.

2017-11-01

The Southern Ocean is of outsized significance to the global oxygen and carbon cycles with relatively poor measurement coverage due to harsh winters and seasonal ice cover. In this study, we use recent advances in the parameterization of air-sea oxygen fluxes to analyze 9 years of oxygen data from a recalibrated Argo oxygen data set and from air-calibrated oxygen floats deployed as part of the Southern Ocean Carbon and Climate Observations and Modeling (SOCCOM) project. From this combined data set of 150 floats, we find a total Southern Ocean oxygen sink of -183 ± 80 Tmol yr-1 (positive to the atmosphere), greater than prior estimates. The uptake occurs primarily in the Polar-Frontal Antarctic Zone (PAZ, -94 ± 30 Tmol O2 yr-1) and Seasonal Ice Zone (SIZ, -111 ± 9.3 Tmol O2 yr-1). This flux is driven by wintertime ventilation, with a large portion of the flux in the SIZ passing through regions with fractional sea ice. The Subtropical Zone (STZ) is seasonally driven by thermal fluxes and exhibits a net outgassing of 47 ± 29 Tmol O2 yr-1 that is likely driven by biological production. The Subantarctic Zone (SAZ) uptake is -25 ± 12 Tmol O2 yr-1. Total oxygen fluxes were separated into a thermal and nonthermal component. The nonthermal flux is correlated with net primary production and mixed layer depth in the STZ, SAZ, and PAZ, but not in the SIZ where seasonal sea ice slows the air-sea gas flux response to the entrainment of deep, low-oxygen waters.

Spatiotemporal trends in surface seawater CO2 in the Gulf of Mexico

NASA Astrophysics Data System (ADS)

Kealoha, A. K.; Shamberger, K.

2016-12-01

The Gulf of Mexico (GoM) contains many interconnected ecosystems intimately linked to regional economic stability through fisheries. Yet, numerous human pressures, including eutrophication-induced hypoxia and ocean acidification (OA), threaten the health of this large marine ecosystem. A comprehensive characterization of the drivers of GoM seawater CO2 cycling is required to assess interactions between these local stresses, global climate change, and OA. Several observational and modeling studies have been conducted in an effort to characterize CO2-system trends within the GoM. However, observational studies are limited to specific regions and time-frames, while modeled data are based on parameterizations that often cannot account for all the biogeochemical processes occurring in this complex system. Here, we present a compilation of approximately 510,000 continuous, underway measurements of sea surface temperature, salinity and seawater CO2, collected from 1996-2013 throughout the entire GoM. These data reveal distinct spatial and temporal CO2 trends that are driven primarily by temperature, Mississippi River outflow, biological productivity, and water circulation. For example, during the spring and summer, nutrient input from the Mississippi River stimulates biological productivity that drives surface seawater CO2 below atmospheric levels in the north-central GoM shelf waters. Although open ocean waters are generally a source of CO2 to the atmosphere in the summer, a unique combination of physical processes including high river discharge, offshore currents and eddy activity can transport low CO2 coastal water beyond the shelf causing vast areas, tens of thousands of square kilometers, of the open ocean to switch to a CO2 sink for several months. Since anthropogenic-driven climate change is expected to influence ocean circulation patterns, GoM CO2 source-sink characteristics and regional scale ocean carbon budgets may be altered in the future. We also combine discrete CO2 chemistry data collected in the Flower Garden Banks National Marine Sanctuary with historical underway data to provide insight into the connections between Gulf wide carbon variability and variability within these important coral reef ecosystems.

Investigating glacial mass balance variability around the Prince Gustav Channel

NASA Astrophysics Data System (ADS)

Royston, Samantha; Gudmundsson, Hilmar; Clarke, Lucy; Fox, Adrian

2015-04-01

Glaciers on the Antarctic Peninsula have shown a varied response to recent climatic change. Most commonly, AP tidewater glaciers have retreated at the calving front and their flow rate has accelerated, increasing the contribution to sea level rise. Here, we utilise the results from a new photogrammetric technique that unlocks the archives of aerial photography from the 1940's to present, to investigate the driving mechanisms of glacier mass change on the AP over this period. Surface DEMs at different epochs have been derived using the new technique for a number of individual glacier basins. A higher-order vertically-integrated ice stream model is used to investigate the driving mechanisms of change for the area around the Prince Gustav Channel, incorporating basins covered by the new datasets. The Prince Gustav Ice Shelf collapsed in January 1995, followed by significant frontal retreat and speed up of its tributary glaciers. Additionally, significant changes have been observed for non-tributary glaciers such as Whisky Glacier on James Ross Island. Here, we investigate the sensitivity of this region's glaciers to ice shelf collapse, atmospheric and oceanic variability.

Modeling and experiments on the drive characteristics of high-strength water hydraulic artificial muscles

NASA Astrophysics Data System (ADS)

Zhang, Zengmeng; Hou, Jiaoyi; Ning, Dayong; Gong, Xiaofeng; Gong, Yongjun

2017-05-01

Fluidic artificial muscles are popular in robotics and function as biomimetic actuators. Their pneumatic version has been widely investigated. A novel water hydraulic artificial muscle (WHAM) with high strength is developed in this study. WHAMs can be applied to underwater manipulators widely used in ocean development because of their environment-friendly characteristics, high force-to-weight ratio, and good bio-imitability. Therefore, the strength of WHAMs has been improved to fit the requirements of underwater environments and the work pressure of water hydraulic components. However, understanding the mechanical behaviors of WHAMs is necessary because WHAMs use work media and pressure control that are different from those used by pneumatic artificial muscles. This paper presents the static and dynamic characteristics of the WHAM system, including the water hydraulic pressure control circuit. A test system is designed and built to analyze the drive characteristics of the developed WHAM. The theoretical relationships among the amount of contraction, pressure, and output drawing force of the WHAM are tested and verified. A linearized transfer function is proposed, and the dynamic characteristics of the WHAM are investigated through simulation and inertia load experiments. Simulation results agree with the experimental results and show that the proposed model can be applied to the control of WHAM actuators.

The tropical Pacific as a key pacemaker of the variable rates of global warming

NASA Astrophysics Data System (ADS)

Kosaka, Yu; Xie, Shang-Ping

2016-09-01

Global mean surface temperature change over the past 120 years resembles a rising staircase: the overall warming trend was interrupted by the mid-twentieth-century big hiatus and the warming slowdown since about 1998. The Interdecadal Pacific Oscillation has been implicated in modulations of global mean surface temperatures, but which part of the mode drives the variability in warming rates is unclear. Here we present a successful simulation of the global warming staircase since 1900 with a global ocean-atmosphere coupled model where tropical Pacific sea surface temperatures are forced to follow the observed evolution. Without prescribed tropical Pacific variability, the same model, on average, produces a continual warming trend that accelerates after the 1960s. We identify four events where the tropical Pacific decadal cooling markedly slowed down the warming trend. Matching the observed spatial and seasonal fingerprints we identify the tropical Pacific as a key pacemaker of the warming staircase, with radiative forcing driving the overall warming trend. Specifically, tropical Pacific variability amplifies the first warming epoch of the 1910s-1940s and determines the timing when the big hiatus starts and ends. Our method of removing internal variability from the observed record can be used for real-time monitoring of anthropogenic warming.

Seasonal characteristics of water exchange in Beibu Gulf based on a particle tracking model

NASA Astrophysics Data System (ADS)

Wang, L.; Pan, W.; Yan, X.

2016-12-01

A lagrangian particle tracking model coupled with a three-dimensional Marine Environmental Committee Ocean Model (MEC) is used to study the transport and seasonal characteristics of water exchange in Beibu Gulf. The hydrodynamic model (MEC), which is forced with the daily surface and lateral boundary fluxes, as well as tidal harmonics and monthly climatological river discharges, is applied to simulate the flow field in the gulf during 2014. Using these results, particle tracking method which includes tidal advection and random walk in the horizontal is used to determine the residence times of sub regions within the gulf in response of winter and summer wind forcing. The result shows water exchange processes in the gulf have a similar tendency with seasonal circulation structure. During the sourthwestly prevailing wind in summer, water particles are traped within the gulf that considerably increases the residence time of each sub region. On the contrary, the presence of strong northeastly prevailing wind in winter drives particles to move cyclonicly leading to shorter residence times and rather active water exchanges among sub regions. Similarly, particle tracking is applied to investigate the water transport in Beibu Gulf. As Qiongzhou Strait and the wide opening in the south of the gulf are two significant channels connecting with the open ocean, continuous particle releases are simulated to quantify the influence range and the pathways of these sources water flowing into Beibu Gulf. The results show that water particles originated from Qiongzhou Strait are moving westward due to the year-round strong westward flow transportation. Influencing range in the north of the Beibu Gulf is enlarged by winter northeastly wind, however, it is blocked to the Leizhou Peninsula coastal region by summer westly wind. In the south opening, water particles are transported northward into the gulf along Hainan Island and flushed from Vietnam coastal region to the ocean rapidly by the longshore currents.

Low Oxygen and Ocean Acidification on the Vancouver Island Shelf

NASA Astrophysics Data System (ADS)

Bianucci, L.; Denman, K.

2008-12-01

In the recent years hypoxic events have been observed along the west coast of North America (off Oregon and California). Although a common cause of coastal hypoxia is usually anthropogenic eutrophication, in these upwelling regions the advection of oxygen-depleted waters from offshore is a key mechanism. Moreover, the high productivity typical of these margins generates a large flux of sinking particular organic matter. The remineralization of this matter below the euphotic zone produces an elevated consumption of oxygen. When concentrations become lower than certain threshold, hypoxia leads to a major change in the ecosystem and the affected areas are called 'dead zones'. Furthermore, the two processes that drive oxygen levels down (physical upwelling and biological demand) also increase dissolved inorganic carbon in the shelf, which leads to a pH reduction. Ocean acidification and hypoxia can severely affect ecosystems, and the links between these phenomena have not been explored. This presentation will discuss a model study of the carbon and oxygen coupling on the Vancouver Island shelf, with focus on the connection between acidification and hypoxia. Moreover, the role of biology versus physics will be investigated. This region comprises the northern end of the wind-driven upwelling margin off western North America, where low oxygen events have not been extensively studied. However, the proximity to an Oxygen Minimum Zone offshore and the observed decline of oxygen in the Northeast Pacific turns this shelf into a potential candidate to suffer from low-oxygen events. The model used is the Regional Ocean Modeling System (ROMS) in a quasi-2D configuration of the shelf (across-shore section with uniform properties alongshore). The biogeochemical model has carbon, oxygen, and nitrogen as state variables, and includes cycling of dissolved organic matter. Carbon and oxygen cycles are coupled through ecosystem processes such as photosynthesis and remineralization, while they are decoupled by other processes (e.g., nitrification and denitrification).

The effect of stratification and topography on high-frequency internal waves in a continental shelf sea

NASA Astrophysics Data System (ADS)

Domina, Anastasiia; Palmer, Matthew; Vlasenko, Vasil; Sharples, Jonathan; Green, Mattias; Stashchuk, Nataliya

2017-04-01

Internal gravity waves (IWs) have been recognised as one of the main drivers of climate controlling circulation, sustaining fisheries in shelf seas and CO2-pump system. High frequency IWs are particularly important to internal mixing in the shelf seas, where they contain an enhanced fraction of the available baroclinic energy. The origin, generation mechanism, propagation and spatial distribution of these waves are unfortunately still poorly understood since they are difficult to measure and simulate, and are therefore not represented in the vast majority of ocean and climate models. In this study we aim to increase our understanding of high frequency IWs dynamics in shelf seas through a combination of observational (from moorings and ocean gliders) and modelling methods (MITgcm), and test the hypothesis that "Solitary waves are responsible for driving a large fraction of the vertical diffusivity at the shelf edge and adjacent shelf region". A new high-resolution (50m horizontal) MITgcm configuration is employed to identify the generation and propagation of IWs in a regional shelf sea and subsequently identify internal wave generation hotspots by using calculated Froude number and body force maps. We assess the likely impact of changing seasonal and climate forcing on IWs with a range of different density structures. Our model suggests that under increasing stratification, the IW field becomes more energetic at all frequencies, however the increase in energy is not evenly distributed. While energy in the dominant low frequency IWs increase by 20-40%, energy associated with high frequency waves increases by as much as 90%. These model results are compared to varying stratification scenarios from observations made during 2012 and 2013 to interpret the impact on continental shelf sea IW generation and propagation. We use the results from a turbulence enabled ocean glider to assess the impact that this varying wavefield has on internal mixing, and discuss the implications this might have on future climate scenarios.

Thermomechanical Controls on the Success and Failure of Continental Rift Systems

NASA Astrophysics Data System (ADS)

Brune, S.

2017-12-01

Studies of long-term continental rift evolution are often biased towards rifts that succeed in breaking the continent like the North Atlantic, South China Sea, or South Atlantic rifts. However there are many prominent rift systems on Earth where activity stopped before the formation of a new ocean basin such as the North Sea, the West and Central African Rifts, or the West Antarctic Rift System. The factors controlling the success and failure of rifts can be divided in two groups: (1) Intrinsic processes - for instance frictional weakening, lithospheric thinning, shear heating or the strain-dependent growth of rift strength by replacing weak crust with strong mantle. (2) External processes - such as a change of plate divergence rate, the waning of a far-field driving force, or the arrival of a mantle plume. Here I use numerical and analytical modeling to investigate the role of these processes for the success and failure of rift systems. These models show that a change of plate divergence rate under constant force extension is controlled by the non-linearity of lithospheric materials. For successful rifts, a strong increase in divergence velocity can be expected to take place within few million years, a prediction that agrees with independent plate tectonic reconstructions of major Mesozoic and Cenozoic ocean-forming rift systems. Another model prediction is that oblique rifting is mechanically favored over orthogonal rifting, which means that simultaneous deformation within neighboring rift systems of different obliquity and otherwise identical properties will lead to success and failure of the more and less oblique rift, respectively. This can be exemplified by the Cretaceous activity within the Equatorial Atlantic and the West African Rifts that lead to the formation of a highly oblique oceanic spreading center and the failure of the West African Rift System. While in nature the circumstances of rift success or failure may be manifold, simplified numerical and analytical models allow the isolated analysis of various contributing factors and to define a characteristic time scale for each process.

Variations in magmatic processes along the East Greenland volcanic margin

NASA Astrophysics Data System (ADS)

Voss, Max; Schmidt-Aursch, Mechita C.; Jokat, Wilfried

2009-05-01

Seismic velocities and the associated thicknesses of rifted and igneous crust provide key constraints on the rifting history, the differentiation between non-volcanic and volcanic rifted margins, the driving force of magmatism at volcanic margins, that is, active or passive upwelling and the temperature anomaly in the lithosphere. This paper presents two new wide-angle seismic transects of the East Greenland margin and combines the velocity models with a compilation of 30-wide-angle seismic velocity models from several publications along the entire East Greenland margin. Compiled maps show the depth to basement, depth to Moho, crustal thickness and thickness of high velocity lower crust (HVLC; with velocities above 7.0 km s-1). First, we present two new wide-angle seismic transects, which contribute to the compilation at the northeast Greenland margin and over the oceanic crust between Shannon Island and the Greenland Fracture Zone. Velocity models, produced by ray tracing result in total traveltime rms-misfits of 100-120 milliseconds and χ2 values of 3.7 and 2.3 for the northern and southern profiles with respect to the data quality and structural complexity. 2-D gravity modelling is used to verify the structural and lithologic constraints. The northernmost profile, AWI-20030200, reveals a magma starved break-up and a rapidly thinning oceanic crust until magnetic anomaly C21 (47.1 Ma). The southern seismic transect, AWI-20030300, exhibits a positive velocity anomaly associated with the Shannon High, and a basin of up to 15 km depth beneath flood basalts between Shannon Island and the continent-ocean boundary. Break-up is associated with minor crustal thickening and a rapidly decreasing thickness of oceanic crust out to anomaly C21. The continental region is proposed to be only sparsely penetrated by volcanism and not underplated by magmatic material at all compared to the vast amount of magmatism further south. Break-up is proposed to have occurred at the seaward boundaries of the continent-ocean transition zones at between ~50 and ~54 Ma, propagating from north to south based on a joint analysis incorporating transects from the Kejser Franz Joseph Fjord and Godthåb Gulf. Secondly, the variation of the HVLC along the East Greenland margin from 60° to 77°N and from transects of its conjugate margin shows inverted emplacement of prominent landward and seaward HVLC thickness portions from north to south in a distribution chart. The differences in the HVLC distribution are attributed to one or more of the following three models. In the first model it is inferred that a transfer zone/detachment acts as a barrier to northward magma flow. In the second model, underplating results in thicker and highly intruded lower crust with several small-scale feeder dykes that locally increase the lower crustal velocities. In the third model, a second magmatic event associated with the separation of the Jan Mayen microcontinent is considered. Lithospheric-scale inhomogeneities might be responsible for the heterogeneous melt generation, the inversion of the HVLC distribution in continental and oceanic domains and differences in its velocities.

Four-Dimensional Oceanic and Atmosperic Data Assimilation with Tropical Rainfall Measuring Mission Data

NASA Technical Reports Server (NTRS)

Takano, Kenji

1996-01-01

An oceanic data assimilation system which allows to utilize the forthcoming Tropical Rainfall Measuring Mission (TRMM) data has been developed and applied to the Pacific Ocean to produce the velocity field. The assimilated data will be indispensable to examine the effects of rainfall and its variability on the structure and circulation of the tropical oceans and to assess the impact of global warming due to the increase of carbon dioxide on the ocean circulation system and the marine pollution caused by oil spill and ocean damping of radionuclide. The data will also provide the verification for the oceanic and ocean-atmosphere coupled General Circulation Models (GCM's). The system consists of oceanic GCM, analysis scheme and data. In the system the flow field has been determined to be physically consistent with the observed density field and the sea surface winds derived from the Special Sensor Microwave Imagery (SSM/I) data which drive the ocean current. The time integration has been performed for five years until the flow field near the surface attained the steady state starting from the rest ocean with observed temperature and salinity fields, and the SSM/I surface wind velocity. The resultant flow field showed high producibility of the system. Especially the flow near the ocean surface agreed well with available observed data. The system, for the first time, succeeded to produce the eastward subtropical current which has been discovered in the joint investigation on Kuroshio current (CSK) in the 1960s. To verify the quality of the flow field a trajectory analysis has been carried out and compared with the Algos buoy data. BRIEF DESCRIPTION OF THE DATA ASSIMILATION SYSTEM ## Oceanic GCM and analysis scheme--The basic equations are much the same as used for the GCM's, except for the Newtonian damping terms introduced into the prediction equations for the potential temperature and salinity to maintain these fields as observed. The C grid of 2'lat. by 2'long. in horizontal and the 11 vertical levels are applied to the entire Pacific Ocean. At the east and west ocean boundaries the periodic boundary conditions are applied creating fictitious ocean there. The SMAC Method is used to increase the accuracy of mass conservation. * Data--The JODC temperature and salinity data obtained from 1906 to 1988 are used in the system between Long.100'E. and 60'W. The surface wind data are derived from the SSM/I data by Dr-R. Atlas of NASA/GSFC. The data set contains every 6 hours data from July 1987 to June 1989 on the grid of 2'lat. by 2.5'long. The averaged for the whole period and then interpolated into the 2'lat. by 2'long. grid data are used to force the system. The sea bottom topography data was based on the General Bathymetric Chart of the Ocean (GEBCO) supplied by the Canadian Hydrographic Service under contract with the International Hydrographic Organization and International Oceanographic Commission of UNESCO.

Fishing out marine parasites? Impacts of fishing on rates of parasitism in the ocean.

PubMed

Wood, Chelsea L; Lafferty, Kevin D; Micheli, Fiorenza

2010-06-01

Among anthropogenic effects on the ocean, fishing is one of the most pervasive and extends deepest into the past. Because fishing reduces the density of fish (reducing transmission efficiency of directly transmitted parasites), selectively removes large fish (which tend to carry more parasites than small fish), and reduces food web complexity (reducing transmission efficiency of trophically transmitted parasites), the removal of fish from the world's oceans over the course of hundreds of years may be driving a longterm, global decline in fish parasites. There has been growing recognition in recent years that parasites are a critical part of biodiversity and that their loss could substantially alter ecosystem function. Such a loss may be among the last major ecological effects of industrial fishing to be recognized by scientists.

Fishing out marine parasites? Impacts of fishing on rates of parasitism in the ocean

USGS Publications Warehouse

Wood, Chelsea L.; Lafferty, Kevin D.; Micheli, Fiorenza

2010-01-01

Among anthropogenic effects on the ocean, fishing is one of the most pervasive and extends deepest into the past. Because fishing reduces the density of fish (reducing transmission efficiency of directly transmitted parasites), selectively removes large fish (which tend to carry more parasites than small fish), and reduces food web complexity (reducing transmission efficiency of trophically transmitted parasites), the removal of fish from the world’s oceans over the course of hundreds of years may be driving a long-term, global decline in fish parasites. There has been growing recognition in recent years that parasites are a critical part of biodiversity and that their loss could substantially alter ecosystem function. Such a loss may be among the last major ecological effects of industrial fishing to be recognized by scientists.

Aquarius main structure configuration

NASA Astrophysics Data System (ADS)

Eremenko, A.

The Aquarius/SAC-D Observatory is a joint US-Argentine mission to map the salinity at the ocean surface. This information is critical to improving our understanding of two major components of Earth's climate system - the water cycle and ocean circulation. By measuring ocean salinity from space, the Aquarius/SAC-D Mission will provide new insights into how the massive natural exchange of freshwater between the ocean, atmosphere and sea ice influences ocean circulation, weather and climate. Aquarius is the primary instrument on the SAC-D spacecraft. It consists of a Passive Microwave Radiometer to detect the surface emission that is used to obtain salinity and an Active Scatterometer to measure the ocean waves that affect the precision of the salinity measurement. The Aquarius Primary Structure houses instrument electronics, feed assemblies, and supports a deployable boom with a 2.5 m Reflector, and provides the structural interface to the SAC-D Spacecraft. The key challenge for the Aquarius main structure configuration is to satisfy the needs of component accommodations, ensuring that the instrument can meet all operational, pointing, environmental, and launch vehicle requirements. This paper describes the evolution of the Aquarius main structure configuration, the challenges of balancing the conflicting requirements, and the major configuration driving decisions and compromises.

Aquarius Main Structure Configuration

NASA Technical Reports Server (NTRS)

Eremenko, Alexander

2012-01-01

The Aquarius/SAC-D Observatory is a joint US-Argentine mission to map the salinity at the ocean surface. This information is critical to improving our understanding of two major components of Earth's climate system - the water cycle and ocean circulation. By measuring ocean salinity from space, the Aquarius/SAC-D Mission will provide new insights into how the massive natural exchange of freshwater between the ocean, atmosphere and sea ice influences ocean circulation, weather and climate. Aquarius is the primary instrument on the SAC-D spacecraft. It consists of a Passive Microwave Radiometer to detect the surface emission that is used to obtain salinity and an Active Scatterometer to measure the ocean waves that affect the precision of the salinity measurement. The Aquarius Primary Structure houses instrument electronics, feed assemblies, and supports a deployable boom with a 2.5 m Reflector, and provides the structural interface to the SAC-D Spacecraft. The key challenge for the Aquarius main structure configuration is to satisfy the needs of component accommodations, ensuring that the instrument can meet all operational, pointing, environmental, and launch vehicle requirements. This paper describes the evolution of the Aquarius main structure configuration, the challenges of balancing the conflicting requirements, and the major configuration driving decisions and compromises.

The influence of food supply on the response of Olympia oyster larvae to ocean acidification

NASA Astrophysics Data System (ADS)

Hettinger, A.; Sanford, E.; Hill, T. M.; Hosfelt, J. D.; Russell, A. D.; Gaylord, B.

2013-03-01

Increases in atmospheric carbon dioxide drive accompanying changes in the marine carbonate system as carbon dioxide (CO2) enters seawater and alters its pH (termed "ocean acidification"). However, such changes do not occur in isolation, and other environmental factors have the potential to modulate the consequences of altered ocean chemistry. Given that physiological mechanisms used by organisms to confront acidification can be energetically costly, we explored the potential for food supply to influence the response of Olympia oyster (Ostrea lurida) larvae to ocean acidification. In laboratory experiments, we reared oyster larvae under a factorial combination of pCO2 and food level. High food availability offset the negative consequences of elevated pCO2 on larval shell growth and total dry weight. Low food availability, in contrast, exacerbated these impacts. In both cases, effects of food and pCO2 interacted additively rather than synergistically, indicating that they operated independently. Despite the potential for abundant resources to counteract the consequences of ocean acidification, impacts were never completely negated, suggesting that even under conditions of enhanced primary production and elevated food availability, impacts of ocean acidification may still accrue in some consumers.

Continent-arc collision in the Banda Arc imaged by ambient noise tomography

NASA Astrophysics Data System (ADS)

Porritt, Robert W.; Miller, Meghan S.; O'Driscoll, Leland J.; Harris, Cooper W.; Roosmawati, Nova; Teofilo da Costa, Luis

2016-09-01

The tectonic configuration of the Banda region in southeast Asia captures the spatial transition from subduction of Indian Ocean lithosphere to subduction and collision of the Australian continental lithosphere beneath the Banda Arc. An ongoing broadband seismic deployment funded by NSF is aimed at better understanding the mantle and lithospheric structure in the region and the relationship of the arc-continent collision to orogenesis. Here, we present results from ambient noise tomography in the region utilizing this temporary deployment of 30 broadband instruments and 39 permanent stations in Indonesia, Timor Leste, and Australia. We measure dispersion curves for over 21,000 inter-station paths resulting in good recovery of the velocity structure of the crust and upper mantle beneath the Savu Sea, Timor Leste, and the Nusa Tenggara Timur (NTT) region of Indonesia. The resulting three dimensional model indicates up to ∼25% variation in shear velocity throughout the plate boundary region; first-order velocity anomalies are associated with the subducting oceanic lithosphere, subducted Australian continental lithosphere, obducted oceanic sediments forming the core of the island of Timor, and high velocity anomalies in the Savu Sea and Sumba. The structure in Sumba and the Savu Sea is consistent with an uplifting forearc sliver. Beneath the island of Timor, we confirm earlier inferences of pervasive crustal duplexing from surface mapping, and establish a link to underlying structural features in the lowermost crust and uppermost mantle that drive upper crustal shortening. Finally, our images of the volcanic arc under Flores, Wetar, and Alor show high velocity structures of the Banda Terrane, but also a clear low velocity anomaly at the transition between subduction of oceanic and continental lithosphere. Given that the footprint of the Banda Terrane has previously been poorly defined, this model provides important constraints on tectonic reconstructions that formerly have lacked information on the lower crust and uppermost mantle.

The influence of food supply on the response of Olympia oyster larvae to ocean acidification

NASA Astrophysics Data System (ADS)

Hettinger, A.; Sanford, E.; Hill, T. M.; Hosfelt, J. D.; Russell, A. D.; Gaylord, B.

2013-10-01

Increases in atmospheric carbon dioxide drive accompanying changes in the marine carbonate system as carbon dioxide (CO2) enters seawater and alters ocean pH (termed "ocean acidification"). However, such changes do not occur in isolation, and other environmental factors have the potential to modulate the consequences of altered ocean chemistry. Given that physiological mechanisms used by organisms to confront acidification can be energetically costly, we explored the potential for food supply to influence the response of Olympia oyster (Ostrea lurida) larvae to ocean acidification. In laboratory experiments, we reared oyster larvae under a factorial combination of pCO2 and food level. Elevated pCO2 had negative effects on larval growth, total dry weight, and metamorphic success, but high food availability partially offset these influences. The combination of elevated pCO2 and low food availability led to the greatest reduction in larval performance. However, the effects of food and pCO2 interacted additively rather than synergistically, indicating that they operated independently. Despite the potential for abundant resources to counteract the consequences of ocean acidification, impacts were never completely negated, suggesting that even under conditions of enhanced primary production and elevated food availability, impacts of ocean acidification may still accrue in some consumers.

Coral Carbonic Anhydrases: Regulation by Ocean Acidification.

PubMed

Zoccola, Didier; Innocenti, Alessio; Bertucci, Anthony; Tambutté, Eric; Supuran, Claudiu T; Tambutté, Sylvie

2016-06-03

Global change is a major threat to the oceans, as it implies temperature increase and acidification. Ocean acidification (OA) involving decreasing pH and changes in seawater carbonate chemistry challenges the capacity of corals to form their skeletons. Despite the large number of studies that have investigated how rates of calcification respond to ocean acidification scenarios, comparatively few studies tackle how ocean acidification impacts the physiological mechanisms that drive calcification itself. The aim of our paper was to determine how the carbonic anhydrases, which play a major role in calcification, are potentially regulated by ocean acidification. For this we measured the effect of pH on enzyme activity of two carbonic anhydrase isoforms that have been previously characterized in the scleractinian coral Stylophora pistillata. In addition we looked at gene expression of these enzymes in vivo. For both isoforms, our results show (1) a change in gene expression under OA (2) an effect of OA and temperature on carbonic anhydrase activity. We suggest that temperature increase could counterbalance the effect of OA on enzyme activity. Finally we point out that caution must, thus, be taken when interpreting transcriptomic data on carbonic anhydrases in ocean acidification and temperature stress experiments, as the effect of these stressors on the physiological function of CA will depend both on gene expression and enzyme activity.

Evaluation of Simulated Marine Aerosol Production Using the WaveWatchIII Prognostic Wave Model Coupled to the Community Atmosphere Model within the Community Earth System Model

DOE Office of Scientific and Technical Information (OSTI.GOV)

Long, M. S.; Keene, William C.; Zhang, J.

2016-11-08

Primary marine aerosol (PMA) is emitted into the atmosphere via breaking wind waves on the ocean surface. Most parameterizations of PMA emissions use 10-meter wind speed as a proxy for wave action. This investigation coupled the 3 rd generation prognostic WAVEWATCH-III wind-wave model within a coupled Earth system model (ESM) to drive PMA production using wave energy dissipation rate – analogous to whitecapping – in place of 10-meter wind speed. The wind speed parameterization did not capture basin-scale variability in relations between wind and wave fields. Overall, the wave parameterization did not improve comparison between simulated versus measured AOD ormore » Na +, thus highlighting large remaining uncertainties in model physics. Results confirm the efficacy of prognostic wind-wave models for air-sea exchange studies coupled with laboratory- and field-based characterizations of the primary physical drivers of PMA production. No discernible correlations were evident between simulated PMA fields and observed chlorophyll or sea surface temperature.« less

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NOx in the Atmosphere of Early Earth as Electron Acceptors for Life

NASA Astrophysics Data System (ADS)

Wong, M. L.; Charnay, B.; Gao, P.; Yung, Y. L.; Russell, M. J.

2015-12-01

We quantify the amount of NOx produced in the Hadean atmosphere and available in the Hadean ocean for the emergence of life. Atmospherically generated nitrate (NO3-) and nitrite (NO2-) are the most attractive high-potential electron acceptors for driving the highly endergonic reactions at the entry points to autotrophic metabolic pathways at submarine alkaline hydrothermal vents (Ducluzeau, 2008; Russell, 2014). The Hadean atmosphere, dominated by CO2 and N2, will produce nitric oxide (NO) when shocked by lightning and impacts (Ducluzeau, 2008; Nna Mvondo, 2001). Photochemical reactions involving NO and H2O vapor will then produce acids such as HNO3 and HNO2 that rain into the ocean and dissociate into NO3- and NO2-. Previous work suggests that 1018 g of NOx can be produced in a million years or so, satisfying the need for micromolar concentrations of NO3- and NO2- in the ocean (Ducluzeau, 2008). But because this number is controversial, we present new calculations based on a novel combination of early-Earth GCM and photochemical modeling, calculating the sources and sinks for fixed nitrogen. Finally, it is notable that lightning has been detected on Venus and Mars along with evidence of atmospheric NO; in the distant past, could NOx have been created and available for the emergence of life on numerous wet, rocky worlds?

Global salinity predictors of western United States precipitation

NASA Astrophysics Data System (ADS)

Liu, T.; Schmitt, R. W.; Li, L.

2016-12-01

Moisture transport from the excess of evaporation over precipitation in the global ocean drives terrestrial precipitation patterns. Sea surface salinity (SSS) is sensitive to changes in ocean evaporation and precipitation, and therefore, to changes in the global water cycle. We use the Met Office Hadley Centre EN4.2.0 SSS dataset to search for teleconnections between autumn-lead seasonal salinity signals and winter precipitation over the western United States. NOAA CPC Unified observational US precipitation in winter months is extracted from bounding boxes over the northwest and southwest and averaged. Lead autumn SON SSS in ocean areas that are relatively highly correlated with winter DJF terrestrial precipitation are filtered by a size threshold and treated as individual predictors. After removing linear trends from the response and explanatory variables and accounting for multiple collinearity, we use best subsets regression and the Bayesian information criterion (BIC) to objectively select the best model to predict terrestrial precipitation using SSS and SST predictors. The combination of autumn SSS and SST predictors can skillfully predict western US winter terrestrial precipitation (R2 = 0.51 for the US Northwest and R2 = 0.7 for the US Southwest). In both cases, SSS is a better predictor than SST. Thus, incorporating SSS can greatly enhance the accuracy of existing precipitation prediction frameworks that use SST-based climate indices and by extension improve watershed management.

Sea Ice Retreat and its Impact on the Intensity of Open-Ocean Convection in the Greenland and Iceland Seas

NASA Astrophysics Data System (ADS)

Moore, K.; Våge, K.; Pickart, R. S.; Renfrew, I.

2016-12-01

The air-sea transfer of heat and freshwater plays a critical role in the global climate system. This is particularly true for the Greenland and Iceland Seas, where these fluxes drive ocean convection that contributes to Denmark Strait Overflow Water, the densest component of the lower limb of the Atlantic Meridional Overturning Circulation (AMOC). This buoyancy transfer is most pronounced during the winter downstream of the ice edge, where the cold and dry Arctic air first comes in contact with the relatively warm ocean surface. Here we show that the wintertime retreat of sea ice in the region, combined with different rates of warming for the atmosphere and sea surface of the Greenland and Iceland Seas, has resulted in statistically significant reductions of approximately 20% in the magnitude of the winter air-sea heat fluxes since 1979. Furthermore, it is demonstrated that modes of climate variability other than the North Atlantic Oscillation (NAO) are required to fully characterize the regional air-sea interaction in this region. Mixed-layer model simulations imply that a continued decrease in atmospheric forcing will exceed a threshold for the Greenland Sea whereby convection will become depth limited, reducing the ventilation of mid-depth waters in the Nordic Seas. In the Iceland Sea, further reductions have the potential to decrease the supply of the densest overflow waters to the AMOC.

The impact of temperature on marine phytoplankton resource allocation and metabolism

NASA Astrophysics Data System (ADS)

Toseland, A.; Daines, S. J.; Clark, J. R.; Kirkham, A.; Strauss, J.; Uhlig, C.; Lenton, T. M.; Valentin, K.; Pearson, G. A.; Moulton, V.; Mock, T.

2013-11-01

Marine phytoplankton are responsible for ~50% of the CO2 that is fixed annually worldwide, and contribute massively to other biogeochemical cycles in the oceans. Their contribution depends significantly on the interplay between dynamic environmental conditions and the metabolic responses that underpin resource allocation and hence biogeochemical cycling in the oceans. However, these complex environment-biome interactions have not been studied on a larger scale. Here we use a set of integrative approaches that combine metatranscriptomes, biochemical data, cellular physiology and emergent phytoplankton growth strategies in a global ecosystems model, to show that temperature significantly affects eukaryotic phytoplankton metabolism with consequences for biogeochemical cycling under global warming. In particular, the rate of protein synthesis strongly increases under high temperatures even though the numbers of ribosomes and their associated rRNAs decreases. Thus, at higher temperatures, eukaryotic phytoplankton seem to require a lower density of ribosomes to produce the required amounts of cellular protein. The reduction of phosphate-rich ribosomes in warmer oceans will tend to produce higher organismal nitrogen (N) to phosphate (P) ratios, in turn increasing demand for N with consequences for the marine carbon cycle due to shifts towards N-limitation. Our integrative approach suggests that temperature plays a previously unrecognized, critical role in resource allocation and marine phytoplankton stoichiometry, with implications for the biogeochemical cycles that they drive.

Population interactions among free-living bluefish and prey fish in an ocean environment.

PubMed

Safina, Carl; Burger, Joanna

1989-04-01

We used sonar to measure relative abundance, location, and depth of prey fish schools (primarily Anchoa and Ammodytes) in the ocean near Fire Island Inlet, New York from May to August for 4 years to examine predatorprey interactions. Prey fish numbers built through May, peaked in June, and thereafter declined coincident with the arrival of predatory bluefish. Bluefish abundance and feeding behavior correlated inversely with prey fish abundance and depth. Bluefish may drive seasonal patterns of prey abundance and distribution in this area through direct predation and by causing prey to flee.

Numerical modeling of storm surges in the coast of Mozambique: the cases of tropical cyclones Bonita (1996) and Lisette (1997)

NASA Astrophysics Data System (ADS)

Bié, Alberto José; de Camargo, Ricardo; Mavume, Alberto Francisco; Harari, Joseph

2017-11-01

The coast of Mozambique is often affected by storms, particularly tropical cyclones during summer or sometimes midlatitude systems in the southern part. Storm surges combined with high freshwater discharge can drive huge coastal floods, affecting both urban and rural areas. To improve the knowledge about the impact of storm surges in the coast of Mozambique, this study presents the first attempt to model this phenomenon through the implementation of the Princeton Ocean Model (POM) in the Southwestern Indian Ocean domain (SWIO; 2-32°S, 28-85°E) using a regular grid with 1/6° of spatial resolution and 36 sigma levels. The simulation was performed for the period 1979-2010, and the most interesting events of surges were related to tropical cyclones Bonita (1996) and Lisette (1997) that occurred in the Mozambique Channel. The results showed that the model represented well the amplitude and phase of principal lunar and solar tidal constituents, as well as it captured the spatial pattern and magnitudes of SST with slight positive bias in summer and negative bias in winter months. In terms of SSH, the model underestimated the presence of mesoscale eddies, mainly in the Mozambique Channel. Our results also showed that the atmospheric sea level pressure had a significant contribution to storm heights during the landfall of the tropical cyclones Bonita (1996) and Lisette (1997) in the coast of Mozambique contributing with about 20 and 16% of the total surge height for each case, respectively, surpassing the contribution of the tide-surge nonlinear interactions by a factor of 2.

Rift systems in the southern North Atlantic: why did some fail and others not?

NASA Astrophysics Data System (ADS)

Nirrengarten, M.; Manatschal, G.; Tugend, J.; Kusznir, N. J.; Sauter, D.

2017-12-01

Orphan, Rockall, Porcupine, Parentis and Pyrenean Basins are failed rift systems surrounding the southern North Atlantic Ocean. The failure or succeessing of a rift system is intimately linked to the question of what controls lithospheric breakup and what keeps oceanic spreading alive. Extension rates and the thermal structure are usually the main parameters invoked. However, between the rifts that succeeded and those that failed, the relative control and relative importance of these parameters is not clear. Cessation of driving forces, strain hardening or competition between concurrent rifts are hypotheses often used to explain rift failure. In this work, we aim to analyze the influence of far field forces on the abandon of rift systems in the southern North Atlantic domain using plate kinematic modeling. A new reconstruction approach that integrates the spatio-temporal evolution of rifted basins has been developed. The plate modeling is based on the definition, mapping and restoration of rift domains using 3D gravity inversions methods that provide crustal thickness maps. The kinematic description of each rift system enables us to discuss the local rift evolution relative to the far field kinematic framework. The resulting model shows a strong segmentation of the different rift systems during extreme crustal thinning that are crosscut by V-shape propagators linked to the exhumation of mantle and emplacement of first oceanic crust. The northward propagating lithospheric breakup of the southern North Atlantic may be partly triggered and channeled by extreme lithospheric thinning. However, at Aptian-Albian time, the northward propagating lithospheric breakup diverts and is partitioned along a transtensional system resulting in the abandon of the Orphan and Rockall basins. The change in the propagation direction may be related to a local strain weakening along existing/inherited transfer zones and/or, alternatively, to a more global plate reorganization. The cessation of the Bay of Biscay-Pyrenean system is related to the northward motion of Africa at Campanian/Santonian time, resulting in a competition between incipient seafloor spreading and far field forces. A concordance between far field forces, lithospheric architecture and strain weakening seems necessary to create a sustainable oceanic domain.

The great 2012 Arctic Ocean summer cyclone enhanced biological productivity on the shelves

PubMed Central

Zhang, Jinlun; Ashjian, Carin; Campbell, Robert; Hill, Victoria; Spitz, Yvette H; Steele, Michael

2014-01-01

[1] A coupled biophysical model is used to examine the impact of the great Arctic cyclone of early August 2012 on the marine planktonic ecosystem in the Pacific sector of the Arctic Ocean (PSA). Model results indicate that the cyclone influences the marine planktonic ecosystem by enhancing productivity on the shelves of the Chukchi, East Siberian, and Laptev seas during the storm. Although the cyclone's passage in the PSA lasted only a few days, the simulated biological effects on the shelves last 1 month or longer. At some locations on the shelves, primary productivity (PP) increases by up to 90% and phytoplankton biomass by up to 40% in the wake of the cyclone. The increase in zooplankton biomass is up to 18% on 31 August and remains 10% on 15 September, more than 1 month after the storm. In the central PSA, however, model simulations indicate a decrease in PP and plankton biomass. The biological gain on the shelves and loss in the central PSA are linked to two factors. (1) The cyclone enhances mixing in the upper ocean, which increases nutrient availability in the surface waters of the shelves; enhanced mixing in the central PSA does not increase productivity because nutrients there are mostly depleted through summer draw down by the time of the cyclone's passage. (2) The cyclone also induces divergence, resulting from the cyclone's low-pressure system that drives cyclonic sea ice and upper ocean circulation, which transports more plankton biomass onto the shelves from the central PSA. The simulated biological gain on the shelves is greater than the loss in the central PSA, and therefore, the production on average over the entire PSA is increased by the cyclone. Because the gain on the shelves is offset by the loss in the central PSA, the average increase over the entire PSA is moderate and lasts only about 10 days. The generally positive impact of cyclones on the marine ecosystem in the Arctic, particularly on the shelves, is likely to grow with increasing summer cyclone activity if the Arctic continues to warm and the ice cover continues to shrink. PMID:26213671

The Role of Precipitation Recycling in the Propagation and Intensification of Droughts in North America

NASA Astrophysics Data System (ADS)

Herrera-Estrada, J. E.; Sheffield, J.; Martinez-Agudelo, J. A.; Dominguez, F.; Wood, E. F.

2017-12-01

Predicting droughts allows stakeholders to mitigate some of the negative impacts of these natural disasters. However, there are still large gaps of knowledge regarding the physical drivers of drought onset, development, and recovery. These gaps have limited our ability to predict some important droughts and to understand how they may be affected by climate change. One physical mechanism that has been linked to the evolution of droughts is precipitation recycling, but its role has not been quantified in detail. Here we use a precipitation recycling model that backtracks the spatial origins of precipitation using vertically integrated moisture fluxes and evapotranspiration data. This allows us to estimate the climatology of moisture sources and sinks, and identify from where moisture fails to arrive when a given region experiences a drought. ERA-Interim data is used to drive this precipitation recycling model from 1980 to 2016 throughout North America and its surrounding oceans. The climatological analysis shows that oceans contribute around 80% of the precipitation over North America during winter, while precipitation that originates from evapotranspiration over land reaches a relative contribution of 60% in the summer. Precipitation contributions from the Pacific Ocean were found to be significantly and positively correlated with ENSO and PDO indices. Furthermore, a regression analysis showed that dry soil moisture in the US Southwest reduces moisture exports to the US Midwest, which in turn can dry soil moisture in the US Midwest. Given that up to 13% of precipitation over the US Midwest was found to be locally recycled, there is a multiplier effect whereby a 10 mm/month reduction in precipitation imports into the region leads to an additional decrease of 0.8 mm/month (on average) from reduced local precipitation recycling, causing a drought to intensify. It was also found that during extensive droughts (e.g. 2011 in Texas and 2012 in the US Midwest), precipitation deficits from land were as large and sometimes larger than those from the oceans. These results demonstrate a mechanism by which droughts can propagate spatially downwind, and point out to processes that need to be captured accurately by models used in operational seasonal forecasting and in climate change studies.

The great 2012 Arctic Ocean summer cyclone enhanced biological productivity on the shelves.

PubMed

Zhang, Jinlun; Ashjian, Carin; Campbell, Robert; Hill, Victoria; Spitz, Yvette H; Steele, Michael

2014-01-01

[1] A coupled biophysical model is used to examine the impact of the great Arctic cyclone of early August 2012 on the marine planktonic ecosystem in the Pacific sector of the Arctic Ocean (PSA). Model results indicate that the cyclone influences the marine planktonic ecosystem by enhancing productivity on the shelves of the Chukchi, East Siberian, and Laptev seas during the storm. Although the cyclone's passage in the PSA lasted only a few days, the simulated biological effects on the shelves last 1 month or longer. At some locations on the shelves, primary productivity (PP) increases by up to 90% and phytoplankton biomass by up to 40% in the wake of the cyclone. The increase in zooplankton biomass is up to 18% on 31 August and remains 10% on 15 September, more than 1 month after the storm. In the central PSA, however, model simulations indicate a decrease in PP and plankton biomass. The biological gain on the shelves and loss in the central PSA are linked to two factors. (1) The cyclone enhances mixing in the upper ocean, which increases nutrient availability in the surface waters of the shelves; enhanced mixing in the central PSA does not increase productivity because nutrients there are mostly depleted through summer draw down by the time of the cyclone's passage. (2) The cyclone also induces divergence, resulting from the cyclone's low-pressure system that drives cyclonic sea ice and upper ocean circulation, which transports more plankton biomass onto the shelves from the central PSA. The simulated biological gain on the shelves is greater than the loss in the central PSA, and therefore, the production on average over the entire PSA is increased by the cyclone. Because the gain on the shelves is offset by the loss in the central PSA, the average increase over the entire PSA is moderate and lasts only about 10 days. The generally positive impact of cyclones on the marine ecosystem in the Arctic, particularly on the shelves, is likely to grow with increasing summer cyclone activity if the Arctic continues to warm and the ice cover continues to shrink.

The numerics of hydrostatic structured-grid coastal ocean models: State of the art and future perspectives

NASA Astrophysics Data System (ADS)

Klingbeil, Knut; Lemarié, Florian; Debreu, Laurent; Burchard, Hans

2018-05-01

The state of the art of the numerics of hydrostatic structured-grid coastal ocean models is reviewed here. First, some fundamental differences in the hydrodynamics of the coastal ocean, such as the large surface elevation variation compared to the mean water depth, are contrasted against large scale ocean dynamics. Then the hydrodynamic equations as they are used in coastal ocean models as well as in large scale ocean models are presented, including parameterisations for turbulent transports. As steps towards discretisation, coordinate transformations and spatial discretisations based on a finite-volume approach are discussed with focus on the specific requirements for coastal ocean models. As in large scale ocean models, splitting of internal and external modes is essential also for coastal ocean models, but specific care is needed when drying & flooding of intertidal flats is included. As one obvious characteristic of coastal ocean models, open boundaries occur and need to be treated in a way that correct model forcing from outside is transmitted to the model domain without reflecting waves from the inside. Here, also new developments in two-way nesting are presented. Single processes such as internal inertia-gravity waves, advection and turbulence closure models are discussed with focus on the coastal scales. Some overview on existing hydrostatic structured-grid coastal ocean models is given, including their extensions towards non-hydrostatic models. Finally, an outlook on future perspectives is made.

Image processing to optimize wave energy converters

NASA Astrophysics Data System (ADS)

Bailey, Kyle Marc-Anthony

The world is turning to renewable energies as a means of ensuring the planet's future and well-being. There have been a few attempts in the past to utilize wave power as a means of generating electricity through the use of Wave Energy Converters (WEC), but only recently are they becoming a focal point in the renewable energy field. Over the past few years there has been a global drive to advance the efficiency of WEC. Placing a mechanical device either onshore or offshore that captures the energy within ocean surface waves to drive a mechanical device is how wave power is produced. This paper seeks to provide a novel and innovative way to estimate ocean wave frequency through the use of image processing. This will be achieved by applying a complex modulated lapped orthogonal transform filter bank to satellite images of ocean waves. The complex modulated lapped orthogonal transform filterbank provides an equal subband decomposition of the Nyquist bounded discrete time Fourier Transform spectrum. The maximum energy of the 2D complex modulated lapped transform subband is used to determine the horizontal and vertical frequency, which subsequently can be used to determine the wave frequency in the direction of the WEC by a simple trigonometric scaling. The robustness of the proposed method is provided by the applications to simulated and real satellite images where the frequency is known.