First record of Naushonia sp. (Decapoda: Laomediidae) larva from the Equatorial Atlantic.

PubMed

De Albuquerque Lira, Simone Maria; De Santana, Claudeilton Severino; Schwamborn, Ralf

2018-02-26

The first zoeal-stage larva of a possibly new species of mud shrimp Naushonia (Decapoda: Gebiidea: Laomediidae) was described from plankton samples taken off the Fernando de Noronha Archipelago, being the first occurrence at the oceanic islands of the Equatorial Atlantic. Five zoea I larvae were obtained and dissected for observation of mouthparts. This zoea I of Naushonia sp. is well distinguished from the first larvae of N. portoricensis (Rathbun 1901) from the Caribbean and N. cangronoides (Kingsley 1897) from the Northwest Atlantic in terms of development and setation of appendages, and possibly belongs to a new, undescribed species. The present study widens the knowledge on tropical oceanic decapod larvae and provides detailed drawings and new photographic illustrations with extended depth of field of these organisms.

Eocene Temperature Evolution of the Tropical Atlantic Ocean

NASA Astrophysics Data System (ADS)

Cramwinckel, M.; Kocken, I.; Agnini, C.; Huber, M.; van der Ploeg, R.; Frieling, J.; Bijl, P.; Peterse, F.; Roehl, U.; Bohaty, S. M.; Schouten, S.; Sluijs, A.

2016-12-01

The transition from the early Eocene ( 50 Ma) hothouse towards the Oligocene ( 33 Ma) icehouse was interrupted by the Middle Eocene Climatic Optimum (MECO) ( 40 Ma), a 500,000-year long episode of deep sea and Southern Ocean warming. It remains unclear whether this transient warming event was global, and whether it was caused by changes in atmospheric greenhouse gas concentrations or confined to high latitudes resulting from ocean circulation change. Here we show, based on biomarker paleothermometry applied at Ocean Drilling Program Site 959, offshore Ghana, that sea surface temperatures in the eastern equatorial Atlantic Ocean declined by 7°C over the middle-late Eocene, in agreement with temperature trends documented in the southern high latitudes. In the equatorial Atlantic, this long-term trend was punctuated by 2.5°C warming during the MECO. At the zenith of MECO warmth, changes in dinoflagellate cyst assemblages and laminated sediments at Site 959 point to open ocean hyperstratification and seafloor deoxygenation, respectively. Remarkably, the data reveal that the magnitude of temperature change in the tropics was approximately half that in the Southern Ocean. This suggests that the generally ice free Eocene yielded limited but significant polar amplification of climate change. Crucially, general circulation model (GCM) simulations reveal that the recorded tropical and deep ocean temperature trends are best explained by greenhouse gas forcing, controlling both middle-late Eocene cooling and the superimposed MECO warming.

Revisiting the Ceara Rise, equatorial Atlantic Ocean: isotope stratigraphy of ODP Leg 154 from 0 to 5 Ma

NASA Astrophysics Data System (ADS)

Wilkens, Roy H.; Westerhold, Thomas; Drury, Anna J.; Lyle, Mitchell; Gorgas, Thomas; Tian, Jun

2017-07-01

Isotope stratigraphy has become the method of choice for investigating both past ocean temperatures and global ice volume. Lisiecki and Raymo (2005) published a stacked record of 57 globally distributed benthic δ18O records versus age (LR04 stack). In this study LR04 is compared to high-resolution records collected at all of the sites drilled during ODP Leg 154 on the Ceara Rise, in the western equatorial Atlantic Ocean. Newly developed software is used to check data splices of the Ceara Rise sites and better align out-of-splice data with in-splice data. Core images recovered from core table photos are depth and age scaled and greatly assist in the data analysis. The entire splices of ODP sites 925, 926, 927, 928 and 929 were reviewed. Most changes were minor although several were large enough to affect age models based on orbital tuning. A Ceara Rise composite record of benthic δ18O is out of sync with LR04 between 1.80 and 1.90 Ma, where LR04 exhibits two maxima but Ceara Rise data contain only one. The interval between 4.0 and 4.5 Ma in the Ceara Rise compilation is decidedly different from LR04, reflecting both the low amplitude of the signal over this interval and the limited amount of data available for the LR04 stack. A regional difference in benthic δ18O of 0.2 ‰ relative to LR04 was found. Independent tuning of Site 926 images and physical property data to the Laskar et al. (2004) orbital solution and integration of available benthic stable isotope data from the Ceara Rise provides a new regional reference section for the equatorial Atlantic covering the last 5 million years.

Revisiting tropical instability wave variability in the Atlantic ocean using SODA reanalysis

NASA Astrophysics Data System (ADS)

de Decco, Hatsue Takanaca; Torres Junior, Audalio Rebelo; Pezzi, Luciano Ponzi; Landau, Luiz

2018-03-01

The spatial and temporal variability of energy exchange in Tropical Instability Waves (TIWs) in the Atlantic Ocean were investigated. A spectral analysis was used to filter the 5-day mean results from Simple Ocean Data Assimilation (SODA) reanalysis spanning from 1958 to 2008. TIWs were filtered over periods of 15 to 60 days and between wavelengths of 4 and 20 longitude degrees. The main approach of this study was the use of bidirectionally filtered TIW time series as the perturbation fields, and the difference in these time series from the SODA total results was considered to be the basic state for energetics analysis. The main result was that the annual cycle (period of 360 days) was the main source of variability of the waves, and the semi-annual cycle (period of 180 days) was a secondary variation, which indicated that TIWs occurred throughout the year but with intensity that varies seasonally. In SODA, barotropic instability acts as the mechanism that feeds and extracts energy to/from TIWs at equatorial Atlantic. Baroclinic instability is the main mechanism that extracts energy from TIWs to the equatorial circulation north of the Equator. All TIW patterns of variability were observed western of 10° W. The present study reveals new evidences regarding TIW variability and suggests that future investigations should include a detailed description of TIW dynamics as part of Atlantic Ocean equatorial circulation.

Contributions of the atmosphere-land and ocean-sea ice model components to the tropical Atlantic SST bias in CESM1

NASA Astrophysics Data System (ADS)

Song, Z.; Lee, S. K.; Wang, C.; Kirtman, B. P.; Qiao, F.

2016-02-01

In order to identify and quantify intrinsic errors in the atmosphere-land and ocean-sea ice model components of the Community Earth System Model version 1 (CESM1) and their contributions to the tropical Atlantic sea surface temperature (SST) bias in CESM1, we propose a new method of diagnosis and apply it to a set of CESM1 simulations. Our analyses of the model simulations indicate that both the atmosphere-land and ocean-sea ice model components of CESM1 contain large errors in the tropical Atlantic. When the two model components are fully coupled, the intrinsic errors in the two components emerge quickly within a year with strong seasonality in their growth rates. In particular, the ocean-sea ice model contributes significantly in forcing the eastern equatorial Atlantic warm SST bias in early boreal summer. Further analysis shows that the upper thermocline water underneath the eastern equatorial Atlantic surface mixed layer is too warm in a stand-alone ocean-sea ice simulation of CESM1 forced with observed surface flux fields, suggesting that the mixed layer cooling associated with the entrainment of upper thermocline water is too weak in early boreal summer. Therefore, although we acknowledge the potential importance of the westerly wind bias in the western equatorial Atlantic and the low-level stratus cloud bias in the southeastern tropical Atlantic, both of which originate from the atmosphere-land model, we emphasize here that solving those problems in the atmosphere-land model alone does not resolve the equatorial Atlantic warm bias in CESM1.

Tropical Atlantic climate response to different freshwater input in high latitudes with an ocean-only general circulation model

NASA Astrophysics Data System (ADS)

Men, Guang; Wan, Xiuquan; Liu, Zedong

2016-10-01

Tropical Atlantic climate change is relevant to the variation of Atlantic meridional overturning circulation (AMOC) through different physical processes. Previous coupled climate model simulation suggested a dipole-like SST structure cooling over the North Atlantic and warming over the South Tropical Atlantic in response to the slowdown of the AMOC. Using an ocean-only global ocean model here, an attempt was made to separate the total influence of various AMOC change scenarios into an oceanic-induced component and an atmospheric-induced component. In contrast with previous freshwater-hosing experiments with coupled climate models, the ocean-only modeling presented here shows a surface warming in the whole tropical Atlantic region and the oceanic-induced processes may play an important role in the SST change in the equatorial south Atlantic. Our result shows that the warming is partly governed by oceanic process through the mechanism of oceanic gateway change, which operates in the regime where freshwater forcing is strong, exceeding 0.3 Sv. Strong AMOC change is required for the gateway mechanism to work in our model because only when the AMOC is sufficiently weak, the North Brazil Undercurrent can flow equatorward, carrying warm and salty north Atlantic subtropical gyre water into the equatorial zone. This threshold is likely to be model-dependent. An improved understanding of these issues may have help with abrupt climate change prediction later.

Turbidity distribution in the Atlantic Ocean

USGS Publications Warehouse

Eittreim, S.; Thorndike, E.M.; Sullivan, L.

1976-01-01

The regional coverage of Lamont nephelometer data in the North and South Atlantic can be used to map seawater turbidity at all depths. At the level of the clearest water, in the mid-depth regions, the turbidity distribution primarily reflects the pattern of productivity in the surface waters. This suggests that the 'background' turbidity level in the oceans is largely a function of biogenic fallout. The bottom waters of the western Atlantic generally exhibit large increases in turbidity. The most intense benthic nepheloid layers are in the southwestern Argentine basin and northern North American basin; the lowest bottom water turbidity in the western Atlantic is in the equatorial regions. Both the Argentine and North American basin bottom waters appear to derive their high turbidity largely from local resuspension of terrigenous input in these basins. In contrast to the west, the eastern Atlantic basins show very low turbidities with the exception of three regions: the Mediterranean outflow area, the Cape basin, and the West European basin. ?? 1976.

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 Ni

Ecological dispersal barrier across the equatorial Atlantic in a migratory planktonic copepod

NASA Astrophysics Data System (ADS)

Goetze, Erica; Hüdepohl, Patricia T.; Chang, Chantel; Van Woudenberg, Lauren; Iacchei, Matthew; Peijnenburg, Katja T. C. A.

2017-11-01

Resolving the large-scale genetic structure of plankton populations is important to understanding their responses to climate change. However, few studies have reported on the presence and geographic extent of genetically distinct populations of marine zooplankton at ocean-basin scales. Using mitochondrial sequence data (mtCOI, 718 animals) from 18 sites across a basin-scale Atlantic transect (39°N-40°S), we show that populations of the dominant migratory copepod, Pleuromamma xiphias, are genetically subdivided across subtropical and tropical waters (global FST = 0.15, global ΦST = 0.21, both P < 0.00001), with a major genetic break observed in the equatorial Atlantic (between gyre FCT and ΦCT = 0.23, P < 0.005). This equatorial region of strong genetic transition coincides with an area of low abundance for the species. Transitional regions between the subtropical gyres and the equatorial province also harbor a distinct mitochondrial clade (clade 2), have higher haplotype and nucleotide diversities relative to the northern and/or southern subtropical gyres (e.g., mean h = 0.831 EQ, 0.742 North, 0.594 South, F2,11 = 20.53, P < 0.001), and are genetically differentiated from the majority of sites in the central gyre and temperate zones of the same hemisphere (significant pairwise ΦST 0.038-0.267, 79% significant). Our observations support the hypothesis that regions of low abundance within species mark areas of suboptimal habitat that serve as dispersal barriers for marine plankton, and we suggest that this may be a dominant mechanism driving the large-scale genetic structure of zooplankton species. Our results also demonstrate the potential importance of the Atlantic equatorial province as a region of evolutionary novelty for the holoplankton.

The Low-Frequency Variability of the Tropical Atlantic Ocean

NASA Technical Reports Server (NTRS)

Haekkinen, Sirpa; Mo, Kingtse C.; Koblinsky, Chester J. (Technical Monitor)

2001-01-01

Upper ocean temperature variability in the tropical Atlantic is examined from the Comprehensive Ocean Atmosphere Data Set (COADS) as well as from an ocean model simulation forced by COADS anomalies appended to a monthly climatology. Our findings are as follows: Only the sea surface temperatures (SST) in the northern tropics are driven by heat fluxes, while the southern tropical variability arises from wind driven ocean circulation changes. The subsurface temperatures in the northern and southern tropics are found to have a strong linkage to buoyancy forcing changes in the northern North Atlantic. Evidence for Kelvin-like boundary wave propagation from the high latitudes is presented from the model simulation. This extratropical influence is associated with wintertime North Atlantic Oscillation (NAO) forcing and manifests itself in the northern and southern tropical temperature anomalies of the same sign at depth of 100-200 meters as result of a Rossby wave propagation away from the eastern boundary in the wake of the boundary wave passage. The most apparent association of the southern tropical sea surface temperature anomalies (STA) arises with the anomalous cross-equatorial winds which can be related to both NAO and the remote influence from the Pacific equatorial region. These teleconnections are seasonal so that the NAO impact on the tropical SST is the largest it mid-winter but in spring and early summer the Pacific remote influence competes with NAO. However, NAO appears to have a more substantial role than the Pacific influence at low frequencies during the last 50 years. The dynamic origin of STA is indirectly confirmed from the SST-heat flux relationship using ocean model experiments which remove either anomalous wind stress forcing or atmospheric forcing anomalies contributing to heat exchange.

Annual, orbital, and enigmatic variations in tropical oceanography recorded by the Equatorial Atlantic amplifier

NASA Technical Reports Server (NTRS)

Mcintyre, Andrew

1992-01-01

Equatorial Atlantic surface waters respond directly to changes in zonal and meridional lower tropospheric winds forced by annual insolation. This mechanism has its maximum effect along the equatorial wave guide centered on 10 deg W. The result is to amplify even subtle tropical climate changes such that they are recorded by marked amplitude changes in the proxy signals. Model realizations, NCAR AGCM and OGCM for 0 Ka and 126 Ka (January and July), and paleoceanographic proxy data show that these winds are also forced by insolation changes at the orbital periods of precession and obliquity. Perhelion in boreal summer produces a strengthened monsoon, e.g., increase meridional and decrease zonal wind stress. This reduces oceanic Ekman divergence and thermocline/nutricline shallowing. The result, in the equatorial Atlantic, is reduced primary productivity and higher euphotic zone temperatures; vice versa for perihelion in boreal winter. Perihelion is controlled by precession. Thus, the dominant period in spectra from a stacked SST record (0-252 Ka BP) at the site of the equatorial Atlantic amplifier is 23 Ky (53 percent of the total variance). This precessional period is coherent (k = 0.920) and in phase with boreal summer insolation. Oscillations of shorter period are present in records from cores sited beneath the amplifier region. These occur between 12.5 and 74.5 Ka BP, when eccentricity modulation of precession is at a minimum. Within this time interval there are 21 cycles with mean periods of 3.0 plus or minus 0.5 Ky. Similar periods have been documented from high latitude regions, e.g., Greenland ice cores from Camp Century. The Camp Century signal in this same time interval contains 21 cycles. A subjective correlation was made between the Camp Century and the equatorial records; the signals were statistically similar, r = 0.722 and k = 0.960.

Diversity and distribution of hyperiid amphipods along a latitudinal transect in the Atlantic Ocean

NASA Astrophysics Data System (ADS)

Burridge, Alice K.; Tump, Marloes; Vonk, Ronald; Goetze, Erica; Peijnenburg, Katja T. C. A.

2017-11-01

As commensals and parasitoids of gelatinous plankton, hyperiid amphipods play unique and important ecological roles in pelagic food webs. Because the diversity and biogeography of this group in oceanic waters is poorly known, we examined diversity and distribution patterns of hyperiids along a basin-scale meridional transect in the Atlantic Ocean (Atlantic Meridional Transect cruise 22). Hyperiids were collected from epipelagic and upper mesopelagic depths at 27 stations between 39°N and 45°S. A total of 70 species in 36 genera and 17 families were identified, the majority of which belonged to the epipelagic Physocephalata infraorder. We observed maximum species and genus richness in the equatorial upwelling region (up to 35 species, 27 genera per station; 7°N-8°S), which appeared largely driven by increased diversity in the superfamily Platysceloidea, as well as a significant and positive relationship between species richness and sea surface temperature. Cluster analyses of hyperiid species assemblages along the transect broadly supported a division into gyral, equatorial, transitional, and subantarctic assemblages, congruent with Longhurst's biogeochemical provinces. Steepest transitions in hyperiid species composition occurred at the southern subtropical convergence zone (34-38°S). The majority of zooplankton groups show maximal diversity in subtropical waters, and our observations of equatorial maxima in species and genus richness for hyperiids suggest that the mechanisms controlling diversity in this group are distinct from other zooplanktonic taxa. These patterns may be driven by the distribution and diversity of gelatinous hosts for hyperiids, which remain poorly characterized at ocean basin scales. The data reported here provide new distributional records for epipelagic and upper mesopelagic hyperiids across six major oceanic provinces in the Atlantic Ocean.

Interannual rainfall variability in the Amazon basin and sea-surface temperatures in the equatorial Pacific and the tropical Atlantic Oceans

NASA Astrophysics Data System (ADS)

Ronchail, Josyane; Cochonneau, Gérard; Molinier, Michel; Guyot, Jean-Loup; Chaves, Adriana Goretti De Miranda; Guimarães, Valdemar; de Oliveira, Eurides

2002-11-01

Rainfall variability in the Amazon basin is studied in relation to sea-surface temperatures (SSTs) in the equatorial Pacific and the northern and southern tropical Atlantic during the 1977-99 period, using the HiBAm original rainfall data set and complementary cluster and composite analyses.The northeastern part of the basin, north of 5 °S and east of 60 °W, is significantly related with tropical SSTs: a rainier wet season is observed when the equatorial Pacific and the northern (southern) tropical Atlantic are anomalously cold (warm). A shorter and drier wet season is observed during El Niño events and negative rainfall anomalies are also significantly associated with a warm northern Atlantic in the austral autumn and a cold southern Atlantic in the spring. The northeastern Amazon rainfall anomalies are closely related with El Niño-southern oscillation during the whole year, whereas the relationships with the tropical Atlantic SST anomalies are mainly observed during the autumn. A time-space continuity is observed between El Niño-related rainfall anomalies in the northeastern Amazon, those in the northern Amazon and south-eastern Amazon, and those in northern South America and in the Nordeste of Brazil.A reinforcement of certain rainfall anomalies is observed when specific oceanic events combine. For instance, when El Niño and cold SSTs in the southern Atlantic are associated, very strong negative anomalies are observed in the whole northern Amazon basin. Nonetheless, the comparison of the cluster and the composite analyses results shows that the rainfall anomalies in the northeastern Amazon are not always associated with tropical SST anomalies.In the southern and western Amazon, significant tropical SST-related rainfall anomalies are very few and spatially variable. The precipitation origins differ from those of the northeastern Amazon: land temperature variability, extratropical perturbations and moisture advection are important rainfall factors, as well

Tropical Dominance of N2 Fixation in the North Atlantic Ocean

NASA Astrophysics Data System (ADS)

Marconi, Dario; Sigman, Daniel M.; Casciotti, Karen L.; Campbell, Ethan C.; Alexandra Weigand, M.; Fawcett, Sarah E.; Knapp, Angela N.; Rafter, Patrick A.; Ward, Bess B.; Haug, Gerald H.

2017-10-01

To investigate the controls on N2 fixation and the role of the Atlantic in the global ocean's fixed nitrogen (N) budget, Atlantic N2 fixation is calculated by combining meridional nitrate fluxes across World Ocean Circulation Experiment sections with observed nitrate 15N/14N differences between northward and southward transported nitrate. N2 fixation inputs of 27.1 ± 4.3 Tg N/yr and 3.0 ± 0.5 Tg N/yr are estimated north of 11°S and 24°N, respectively. That is, 90% of the N2 fixation in the Atlantic north of 11°S occurs south of 24°N in a region with upwelling that imports phosphorus (P) in excess of N relative to phytoplankton requirements. This suggests that, under the modern iron-rich conditions of the equatorial and North Atlantic, N2 fixation occurs predominantly in response to P-bearing, N-poor conditions. We estimate a N2 fixation rate of 30.5 ± 4.9 Tg N/yr north of 30°S, implying only 3 Tg N/yr between 30° and 11°S, despite evidence of P-bearing, N-poor surface waters in this region as well; this is consistent with iron limitation of N2 fixation in the South Atlantic. Since the ocean flows through the Atlantic surface in <2,500 years, similar to the residence time of oceanic fixed N, Atlantic N2 fixation can stabilize the N-to-P ratio of the global ocean. However, the calculated rate of Atlantic N2 fixation is a small fraction of global ocean estimates for either N2 fixation or fixed N loss. This suggests that, in the modern ocean, an approximate balance between N loss and N2 fixation is achieved within the combined Indian and Pacific basins.

Water-mass evolution in the Cretaceous Western Interior Seaway of North America and equatorial Atlantic

NASA Astrophysics Data System (ADS)

Eldrett, James S.; Dodsworth, Paul; Bergman, Steven C.; Wright, Milly; Minisini, Daniel

2017-07-01

The Late Cretaceous Epoch was characterized by major global perturbations in the carbon cycle, the most prominent occurring near the Cenomanian-Turonian (CT) transition marked by Oceanic Anoxic Event 2 (OAE-2) at 94.9-93.7 Ma. The Cretaceous Western Interior Seaway (KWIS) was one of several epicontinental seas in which a complex water-mass evolution was recorded in widespread sedimentary successions. This contribution integrates new data on the main components of organic matter, geochemistry, and stable isotopes along a north-south transect from the KWIS to the equatorial western Atlantic and Southern Ocean. In particular, cored sedimentary rocks from the Eagle Ford Group of west Texas (˜ 90-98 Ma) demonstrate subtle temporal and spatial variations in palaeoenvironmental conditions and provide an important geographic constraint for interpreting water-mass evolution. High-latitude (boreal-austral), equatorial Atlantic Tethyan and locally sourced Western Interior Seaway water masses are distinguished by distinct palynological assemblages and geochemical signatures. The northward migration of an equatorial Atlantic Tethyan water mass into the KWIS occurred during the early-middle Cenomanian (98-95 Ma) followed by a major re-organization during the latest Cenomanian-Turonian (95-94 Ma) as a full connection with a northerly boreal water mass was established during peak transgression. This oceanographic change promoted de-stratification of the water column and improved oxygenation throughout the KWIS and as far south as the Demerara Rise off Suriname. In addition, the recorded decline in redox-sensitive trace metals during the onset of OAE-2 likely reflects a genuine oxygenation event related to open water-mass exchange and may have been complicated by variable contribution of organic matter from different sources (e.g. refractory/terrigenous material), requiring further investigation.

Calculation of wind-driven surface currents in the North Atlantic Ocean

NASA Technical Reports Server (NTRS)

Rees, T. H.; Turner, R. E.

1976-01-01

Calculations to simulate the wind driven near surface currents of the North Atlantic Ocean are described. The primitive equations were integrated on a finite difference grid with a horizontal resolution of 2.5 deg in longitude and latitude. The model ocean was homogeneous with a uniform depth of 100 m and with five levels in the vertical direction. A form of the rigid-lid approximation was applied. Generally, the computed surface current patterns agreed with observed currents. The development of a subsurface equatorial countercurrent was observed.

Wet deposition of trace elements and radon daughter systematics in the South and equatorial Atlantic atmosphere

NASA Astrophysics Data System (ADS)

Kim, Guebuem; Church, Thomas M.

2002-09-01

Atmospheric samples were collected aboard ship in the South and equatorial Atlantic (35°S-10°N) between 19 May and 20 June 1996. We measured 222Rn in air, 210Pb in aerosol, and trace elements (Fe, Mn, Zn, Pb, Cu, Cd, Ni, and Cr), 210Pb, and 210Po in precipitation samples. The large variation of 222Rn in air suggests a significant change in the incursion of continental air with time and latitude in the remote Atlantic. In the equatorial and subtropical Atlantic (20°S-10°N), 222Rn activity was lower but 210Pb/222Rn ratios were higher than those at higher latitudes. The higher 210Pb/222Rn ratios in the equatorial Atlantic appear to be due to prevailing trade easterly winds which transport a supported source of 210Pb in Saharan dust from the African Sahel. The enrichment of noncrustal trace elements in precipitation samples from the remote equatorial Atlantic was small on account of the remoteness from the continental emission regions and as a result of dilution with Saharan dust. The wet depositional fluxes of major crustal elements (Fe and Mn) were two- to three-fold higher, while those of Cd and Zn were two- to ten-fold lower, in the South and equatorial Atlantic relative to the western North Atlantic (Bermuda) or North Atlantic coast (Lewes, Delaware). Thus, dominant wet precipitation of Saharan dust in the Intertropical Convergence Zone (ITCZ) areas of the equatorial Atlantic appears to be a large potential source of micronutrients (i.e., Fe) to surface seawater.

Metagenomic analysis of sediments under seaports influence in the Equatorial Atlantic Ocean.

PubMed

Tavares, Tallita Cruz Lopes; Normando, Leonardo Ribeiro Oliveira; de Vasconcelos, Ana Tereza Ribeiro; Gerber, Alexandra Lehmkuhl; Agnez-Lima, Lucymara Fassarella; Melo, Vânia Maria Maciel

2016-07-01

Maritime ports are anthropogenic interventions capable of causing serious alterations in coastal ecosystems. In this study, we examined the benthic microbial diversity and community structure under the influence of two maritime ports, Mucuripe (MUC) and Pecém (PEC), at Equatorial Atlantic Ocean in Northeast Brazil. Those seaports differ in architecture, time of functioning, cargo handling and contamination. The microbiomes from MUC and PEC were also compared in silico to 11 other globally distributed marine microbiomes. The comparative analysis of operational taxonomic units (OTUs) retrieved by PCR-DGGE showed that MUC presents greater richness and β diversity of Bacteria and Archaea than PEC. In line with these results, metagenomic analysis showed that MUC and PEC benthic microbial communities share the main common bacterial phyla found in coastal environments, although can be distinguish by greater abundance of Cyanobacteria in MUC and Deltaproteobacteria in PEC. Both ports differed in Archaea composition, being PEC port sediments dominated by Thaumarchaeota. The microbiomes showed little divergence in their potential metabolic pathways, although shifts on the microbial taxonomic signatures involved in nitrogen and sulphur metabolic pathways were observed. The comparative analysis of different benthic marine metagenomes from Brazil, Australia and Mexico grouped them by the geographic location rather than by the type of ecosystem, although at phylum level seaport sediments share a core microbiome constituted by Proteobacteria, Cyanobacteria, Actinobacteria, Tenericuteres, Firmicutes, Bacteriodetes and Euryarchaeota. Our results suggest that multiple physical and chemical factors acting on sediments as a result of at least 60years of port operation play a role in shaping the benthic microbial communities at taxonomic level, but not at functional level. Copyright © 2016 Elsevier B.V. All rights reserved.

Evidence for the Maintenance of Slowly Varying Equatorial Currents by Intraseasonal Variability

NASA Astrophysics Data System (ADS)

Greatbatch, Richard J.; Claus, Martin; Brandt, Peter; Matthießen, Jan-Dirk; Tuchen, Franz Philip; Ascani, François; Dengler, Marcus; Toole, John; Roth, Christina; Farrar, J. Thomas

2018-02-01

Recent evidence from mooring data in the equatorial Atlantic reveals that semiannual and longer time scale ocean current variability is close to being resonant with equatorial basin modes. Here we show that intraseasonal variability, with time scales of tens of days, provides the energy to maintain these resonant basin modes against dissipation. The mechanism is analogous to that by which storm systems in the atmosphere act to maintain the atmospheric jet stream. We demonstrate the mechanism using an idealized model setup that exhibits equatorial deep jets. The results are supported by direct analysis of available mooring data from the equatorial Atlantic Ocean covering a depth range of several thousand meters. The analysis of the mooring data suggests that the same mechanism also helps maintain the seasonal variability.

Biomarker Evidence From Demerara Rise for Surface and Deep Water Redox Conditions in the mid Cretaceous Western Equatorial Atlantic

NASA Astrophysics Data System (ADS)

Beckmann, B.; Hofmann, P.; Schouten, S.; Sinninghe Damsté, J. S.; Wagner, T.

2006-12-01

Oceanic Anoxic Events (OAEs) provide deep insights into rapid climate change and atmosphere-land ocean interactions during an extremely warm mode of the Earth system. We present results from ODP Leg 207 at Demerara Rise deposited in the western tropical Atlantic during transition from the Turonian OAE 2 to the Santonian OAE 3. Molecular markers in organic matter-rich black shale identify the composition of primary producers and provide detailed information on the oxygenation state of surface and deep waters. This information is relevant to infer the dynamics and controls of sedimentation leading to black shale in the tropical Atlantic. Bulk organic geochemical data suggest the dominance of lipid-rich marine organic matter throughout the study section. Biomarkers from the aliphatic fraction instead reveal variable contributions of e.g., archaea, diatoms, and dinoflagellates supporting changes in the community of primary producers that thrived in the oxic part of the photic zone in response to changing environmental conditions similar to modern high productive areas along continental margins. Also comparable to modern high productive areas the sea floor remained generally oxygen-depleted throughout the Turonian to Santonian as supported by elevated lycopane contents along with an enrichment of redox-sensitive elements and documented by persistent high TOC concentrations (1 to 14%). Isorenieratane derivates indicative of photic zone euxinia (PZE) were only detected in low abundances in the lowest part of the study section. This observation contrasts biomarker records from the eastern low latitude Atlantic where PZE was a temporal feature determining black shale formation. The new biomarker data from Leg 207 support progressive weakening of upwelling intensity along with oxygenation of surface and possibly mid waters from the upper Coniacian on. Different from black shale sites in many semi-sheltered sub-basins along the Equatorial Atlantic, Demerara Rise was fully

Variability of the Tropical Ocean Surface Temperatures at Decadal-Multidecadal Timescales. Part I: The Atlantic Ocean.

NASA Astrophysics Data System (ADS)

Mehta, Vikram M.

1998-09-01

Gridded time series from the Global Ocean Surface Temperature Atlas were analyzed with a variety of techniques to identify spatial structures and oscillation periods of the tropical Atlantic sea surface temperature (SST) variations at decadal timescales, and to develop physical interpretations of statistical patterns of decadal SST variations. Each time series was 110 yr (1882-1991) long. The tropical Atlantic SST variations were compared with decadal variations in a 74-yr-long (1912-85) north Nordeste Brazil rainfall time series and a 106-yr-long (1886-1991) tropical Atlantic cyclone activity index time series. The tropical Atlantic SST variations were also compared with decadal variations in the extratropical Atlantic SST.Multiyear to multidecadal variations in the cross-equatorial dipole pattern identified as a dominant empirical pattern of the tropical Atlantic SST variations in earlier and present studies are shown to be variations in the approximately north-south gradient of SST anomalies. It is also shown that there was no dynamical-thermodynamical, dipole mode of SST variations during the analysis period. There was a distinct decadal timescale (12-13 yr) of SST variations in the tropical South Atlantic, whereas no distinct decadal timescale was found in the tropical North Atlantic SST variations. Approximately 80% of the coherent decadal variance in the cross-equatorial SST gradient was `explained' by coherent decadal oscillations in the tropical South Atlantic SSTs. There were three, possibly physical, modes of decadal variations in the tropical Atlantic SSTs during the analysis period. In the more energetic mode of the North Atlantic decadal SST variations, anomalies traveled into the tropical North Atlantic from the extratropical North Atlantic along the eastern boundary of the basin. The anomalies strengthened and resided in the tropical North Atlantic for several years, then frequently traveled northward into the mid-high-latitude North Atlantic along

Whale Shark (Rhincodon typus) Seasonal Occurrence, Abundance and Demographic Structure in the Mid-Equatorial Atlantic Ocean.

PubMed

Macena, Bruno C L; Hazin, Fábio H V

2016-01-01

Whale sharks are generally associated with environmental factors that drive their movements to specific locations where food availability is high. Consequently, foraging is believed to be the main reason for the formation of whale shark aggregations. Feeding aggregations occur mainly in nearshore areas and are composed primarily of immature individuals. Conversely, aggregations of mature adults are rarely observed, and their occurrence is correlated with oceanic environments. Despite an increase in the number of whale shark studies, information on mating and parturition grounds is still lacking. In the present work, we assessed the ecological and behavioural aspects of the whale sharks that visit the archipelago of São Pedro and São Paulo (ASPSP), located ~1,000 km off the coast of Brazil in the equatorial Atlantic Ocean. Forty-nine whale sharks were recorded from February 2005 to May 2014. The estimated mean ± SD size was 8.27 ± 2.52 m (range: 2.5-14.0 m) with no significant differences in size across the year. The maturational stages were classified by size as immature (<8.0 m; 32.56%) and mature (>9.0 m; 46.51%); with almost half of the observed animals being mature specimens. The majority of sightings occurred between February and June. During this period, the ocean current weakens and the waters are enriched by eggs and larvae of fishes and invertebrates that attract marine life to forage. At the same time, evidence of reproductive activity in adult females (i.e. swollen abdomen and bite marks on the pectoral fins), and the potential mating behaviour exhibited by one male, suggest that the ASPSP area might also have a role in whale shark reproduction. Irrespective of its use for feeding or reproduction, this insular habitat serves as a meeting point for both juvenile and adult whale sharks, and may play an important ecological role for the species.

Influence of solar radiation absorbed by phytoplankton on the thermal structure and circulation of the tropical Atlantic Ocean

NASA Astrophysics Data System (ADS)

Frouin, Robert; Ueyoshi, Kyozo; Kampel, Milton

2007-09-01

Numerical experiments conducted with an ocean general ocean circulation model reveal the potential influence of solar radiation absorbed by phytoplankton on the thermal structure and currents of the Tropical Atlantic Ocean. In the model, solar radiation penetration is parameterized explicitly as a function of chlorophyll-a concentration, the major variable affecting water turbidity in the open ocean. Two types of runs are performed, a clear water (control) run with a constant minimum chlorophyll-a concentration of 0.02 mgm -3, and a turbid water (chlorophyll) run with space- and time-varying chlorophyll-a concentration from satellite data. The difference between results from the two runs yields the biological effects. In the chlorophyll run, nutrients and biology production are implicitly taken into account, even though biogeochemical processes are not explicitly included, since phytoplankton distribution, prescribed from observations, is the result of those processes. Due to phytoplankton-radiation forcing, the surface temperature is higher by 1-2 K on average annually in the region of the North Equatorial current, the Northern part of the South Equatorial current, and the Caribbean system, and by 3-4 K in the region of the Guinea current. In this region, upwelling is reduced, and heat trapped in the surface layers by phytoplankton is not easily removed. The surface temperature is lower by 1 K in the Northern region of the Benguela current, due to increased upwelling. At depth, the equatorial Atlantic is generally cooler, as well as the eastern part of the tropical basin (excluding the region of the sub-tropical gyres). The North and South equatorial currents, as well as the Equatorial undercurrent, are enhanced by as much as 3-4 cms -1, and the circulation of the subtropical gyres is increased. Pole-ward heat transport is slightly reduced North of 35°N, suggesting that phytoplankton, by increasing the horizontal return flow in the subtropical region, may exert a

Water-rich sublithospheric melt channel in the equatorial Atlantic Ocean

NASA Astrophysics Data System (ADS)

Mehouachi, Fares; Singh, Satish C.

2018-01-01

The lithosphere-asthenosphere boundary is the most extensive boundary on Earth, separating the mobile plate above from the convecting mantle below, but its nature remains a matter of debate. Using an ultra-deep seismic reflection technique, here we show a systematic seismic image of two deep reflectors that we interpret as the upper and lower limits of the lithosphere-asthenosphere boundary beneath a 40-70-million-year-old oceanic lithosphere in the Atlantic Ocean. These two reflections correspond to 1,260 °C and 1,355 °C isotherms and bound a low-velocity channel, suggesting that the lithosphere-asthenosphere boundary is thermally controlled. We observe a clear age dependency of this sublithospheric channel: its depth increases with age from 72 km where it is 40-Myr-old to 88 km where it is 70-Myr-old, whereas its thickness decreases with age from 18 km to 12 km. We suggest that partial melting, facilitated by water, is the main mechanism responsible for the low-velocity channel. The required water concentration for melting increases with age; nevertheless, its corresponding total mass remains relatively constant, suggesting that most of the volatiles in the oceanic sublithospheric channel originate from a horizontal flux near the ridge axis.

Carbon and Neodymium Isotopic Fingerprints of Atlantic Deep Ocean Circulation During the Warm Pliocene

NASA Astrophysics Data System (ADS)

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

2012-12-01

Earth's future climate may resemble the mid-Piacenzian Age of the Pliocene, a time when global temperatures were sustained within the range predicted for the coming century. Surface and deep water 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 surface temperature anomaly in the mid-Piacenzian (3.264 - 3.025 Ma), accompanied by increased evaporation. The anomaly is detected in deep waters at 46°S, suggesting enhanced meridional overturning circulation and more southerly penetration of North Atlantic Deep Water (NADW) during the PRISM interval. However deep water temperature proxies are not diagnostic of water mass and some coupled model simulations predict transient decreases in NADW production in the 21st century, presenting a contrasting picture of future climate. We present a new multi-proxy investigation of Atlantic deep ocean circulation during the warm mid-Piacenzian, using δ13C of benthic foraminifera as a proxy for water mass age and the neodymium isotopic composition of fossil fish teeth (ɛNd) as a proxy for water mass source and mixing. This reconstruction utilizes both new and previously published data from DSDP and ODP cores along equatorial (Ceara Rise), southern mid-latitude (Walvis Ridge), and south Atlantic (Meteor Rise/Agulhas Ridge) depth transects. Additional end-member sites in the regions of modern north Atlantic and Southern Ocean deep water formation provide a Pliocene baseline for comparison. δ13C throughout the Atlantic basin is remarkably homogenous during the PRISM interval. δ13C values of Cibicidoides spp. and C. wuellerstorfi largely range between 0‰ and 1‰ at North Atlantic, shallow equatorial, southern mid-latitude, and south Atlantic sites with water depths from 2000-4700 m; both depth and latitudinal gradients are generally small (~0.3‰). However, equatorial

Studies of the intermediate and deep circulation in the western equatorial Atlantic

NASA Technical Reports Server (NTRS)

Desaubies, Yves; Frankignoul, C.; Merle, Jacques

1991-01-01

This proposal concerns the preparation and design of an experiment, the objective of which is to improve our knowledge of the intermediate and deep circulation in the western equatorial Atlantic Ocean. We shall focus on the description of the western boundary currents, of their crossing with the equator, on the estimation of their mass and heat fluxes, and their seasonal and interannual variations. We will use satellite altimetric data, tomographic measurements, and in situ observations (current measurements, hydrology, and floaters). We propose a feasibility study and the definition of a strategy based on a high-resolution Geophysical Fluid Dynamics Laboratory (GFDL) numerical model to define which in situ measurements are necessary to optimally complete the altimetric observations.

Fracture zones in the equatorial Atlantic and the breakup of western Pangea

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

Jones, E.J.W.

1987-06-01

The early breakup of western Pangea has been investigated by mapping the pattern of fracture zones and distribution of seismic reflectors within the sedimentary cover of the Atlantic between the Cape Verde Islands and the equator. Two distinct sets of transverse oceanic lineaments are present, separated by the Guinea Fracture Zone near lat 10/sup 0/N. Lineaments to the north are associated with the formation of the central Atlantic in the Late Jurassic and Early Cretaceous; those in the south relate to the Cretaceous opening of the South Atlantic. The Guinea Fracture Zone is thus the conjugate of the Jurassic transformmore » boundary under peninsular Florida, which linked the Atlantic with the Gulf of Mexico. The distribution of dated seismic reflectors suggests that deposition of deep-water sediments was confined to the region north of the Guinea transform until Aptian time, when the Sierra Leone Basin began to open. The latter started to widen at least 15 m.y. after the initiation of the Cape Basin off southwest Africa, an age difference that can be explained if a short-lived plate boundary developed in either Africa or South America during the Early Cretaceous. Neither the trends of the equatorial fracture zones nor the seismic stratigraphy supports the existence of a predrift gap between west Africa and Brazil.« less

Whale Shark (Rhincodon typus) Seasonal Occurrence, Abundance and Demographic Structure in the Mid-Equatorial Atlantic Ocean

PubMed Central

Hazin, Fábio H. V.

2016-01-01

Whale sharks are generally associated with environmental factors that drive their movements to specific locations where food availability is high. Consequently, foraging is believed to be the main reason for the formation of whale shark aggregations. Feeding aggregations occur mainly in nearshore areas and are composed primarily of immature individuals. Conversely, aggregations of mature adults are rarely observed, and their occurrence is correlated with oceanic environments. Despite an increase in the number of whale shark studies, information on mating and parturition grounds is still lacking. In the present work, we assessed the ecological and behavioural aspects of the whale sharks that visit the archipelago of São Pedro and São Paulo (ASPSP), located ~1,000 km off the coast of Brazil in the equatorial Atlantic Ocean. Forty-nine whale sharks were recorded from February 2005 to May 2014. The estimated mean ± SD size was 8.27 ± 2.52 m (range: 2.5–14.0 m) with no significant differences in size across the year. The maturational stages were classified by size as immature (<8.0 m; 32.56%) and mature (>9.0 m; 46.51%); with almost half of the observed animals being mature specimens. The majority of sightings occurred between February and June. During this period, the ocean current weakens and the waters are enriched by eggs and larvae of fishes and invertebrates that attract marine life to forage. At the same time, evidence of reproductive activity in adult females (i.e. swollen abdomen and bite marks on the pectoral fins), and the potential mating behaviour exhibited by one male, suggest that the ASPSP area might also have a role in whale shark reproduction. Irrespective of its use for feeding or reproduction, this insular habitat serves as a meeting point for both juvenile and adult whale sharks, and may play an important ecological role for the species. PMID:27783634

African Equatorial and Subtropical Ozone Plumes: Recurrences Timescales of the Brown Cloud Trans-African Plumes and Other Plumes

NASA Technical Reports Server (NTRS)

Chatfield, Robert B.; Thompson, Anne M.; Guan, Hong; Witte, Jacquelyn C.

2004-01-01

We have found repeated illustrations in the maps of Total Tropospheric Ozone (TTO) of apparent transport of ozone from the Indian Ocean to the Equatorial Atlantic Ocean. Most interesting are examples that coincide with the INDOEX observations of late northern winter, 1999. Three soundings associated with the SHADOZ (Southern Hemisphere Additional Ozonesondes) network help confirm and quantify degree of influence of pollution, lightning, and stratospheric sources, suggesting that perhaps 40% of increased Atlantic ozone could be Asian pollution during periods of maximum identified in the TTO maps. We outline recurrent periods of apparent ozone transport from Indian to Atlantic Ocean regions both during and outside the late-winter period. These are placed in the context of some general observations about factors controlling recurrence timescales for the expression of both equatorial and subtropical plumes. Low-level subtropical plumes are often controlled by frontal systems approaching the Namib coast; these direct mid-level air into either easterly equatorial plumes or westerly mid- troposphere plumes. Equatorial plumes of ozone cross Africa on an easterly path due to the occasional coincidence of two phenomena: (1) lofting of ozone to mid and upper levels, often in the Western Indian Ocean, and (2) the eastward extension of an Equatorial African easterly jet.

Seasonal sea surface cooling in the equatorial Pacific cold tongue controlled by ocean mixing.

PubMed

Moum, James N; Perlin, Alexander; Nash, Jonathan D; McPhaden, Michael J

2013-08-01

Sea surface temperature (SST) is a critical control on the atmosphere, and numerical models of atmosphere-ocean circulation emphasize its accurate prediction. Yet many models demonstrate large, systematic biases in simulated SST in the equatorial 'cold tongues' (expansive regions of net heat uptake from the atmosphere) of the Atlantic and Pacific oceans, particularly with regard to a central but little-understood feature of tropical oceans: a strong seasonal cycle. The biases may be related to the inability of models to constrain turbulent mixing realistically, given that turbulent mixing, combined with seasonal variations in atmospheric heating, determines SST. In temperate oceans, the seasonal SST cycle is clearly related to varying solar heating; in the tropics, however, SSTs vary seasonally in the absence of similar variations in solar inputs. Turbulent mixing has long been a likely explanation, but firm, long-term observational evidence has been absent. Here we show the existence of a distinctive seasonal cycle of subsurface cooling via mixing in the equatorial Pacific cold tongue, using multi-year measurements of turbulence in the ocean. In boreal spring, SST rises by 2 kelvin when heating of the upper ocean by the atmosphere exceeds cooling by mixing from below. In boreal summer, SST decreases because cooling from below exceeds heating from above. When the effects of lateral advection are considered, the magnitude of summer cooling via mixing (4 kelvin per month) is equivalent to that required to counter the heating terms. These results provide quantitative assessment of how mixing varies on timescales longer than a few weeks, clearly showing its controlling influence on seasonal cooling of SST in a critical oceanic regime.

75 FR 18778 - Safety Zone; Ocean City Air Show 2010, Atlantic Ocean, Ocean City, MD

Federal Register 2010, 2011, 2012, 2013, 2014

2010-04-13

...-AA00 Safety Zone; Ocean City Air Show 2010, Atlantic Ocean, Ocean City, MD AGENCY: Coast Guard, DHS... zone on the Atlantic Ocean in the vicinity of Ocean City, Maryland to support the Ocean City Air Show..., 5, and 6, 2010 Ocean City, Maryland will host an air show event on the Atlantic Ocean between Talbot...

AtlantOS - Optimizing and Enhancing the Integrated Atlantic Ocean Observing System

NASA Astrophysics Data System (ADS)

Reitz, Anja; Visbeck, Martin; AtlantOS Consortium, the

2016-04-01

Atlantic Ocean observation is currently undertaken through loosely-coordinated, in-situ observing networks, satellite observations and data management arrangements of heterogeneous international, national and regional design to support science and a wide range of information products. Thus there is tremendous opportunity to develop the systems towards a fully integrated Atlantic Ocean Observing System consistent with the recently developed 'Framework of Ocean Observing'. The vision of AtlantOS is to improve and innovate Atlantic observing by using the Framework of Ocean Observing to obtain an international, more sustainable, more efficient, more integrated, and fit-for-purpose system. Hence, the AtlantOS initiative will have a long-lasting and sustainable contribution to the societal, economic and scientific benefit arising from this integrated approach. This will be delivered by improving the value for money, extent, completeness, quality and ease of access to Atlantic Ocean data required by industries, product supplying agencies, scientist and citizens. The overarching target of the AtlantOS initiative is to deliver an advanced framework for the development of an integrated Atlantic Ocean Observing System that goes beyond the state-of -the-art, and leaves a legacy of sustainability after the life of the project. The legacy will derive from the following aims: i) to improve international collaboration in the design, implementation and benefit sharing of ocean observing, ii) to promote engagement and innovation in all aspects of ocean observing, iii) to facilitate free and open access to ocean data and information, iv) to enable and disseminate methods of achieving quality and authority of ocean information, v) to strengthen the Global Ocean Observing System (GOOS) and to sustain observing systems that are critical for the Copernicus Marine Environment Monitoring Service and its applications and vi) to contribute to the aims of the Galway Statement on Atlantic

Multidecadal-scale adjustment of the ocean mixed layer heat budget in the tropics: examining ocean reanalyses

NASA Astrophysics Data System (ADS)

Cook, Kerry H.; Vizy, Edward K.; Sun, Xiaoming

2018-03-01

Distributions of ocean mixed layer temperature trends and trends in the net heat flux from the atmosphere differ, indicating the important role of the transport of heat within the ocean for determining temperature trends. Annual-mean, linear trends in the components of the tropical ocean mixed layer heat budget for 1980-2015 are diagnosed in 4 ocean reanalyses to improve our physical understanding of multidecadal-scale SST trends. The well-known temperature trend in the tropical Pacific, with cooling in the east and warming in the west, is reproduced in each reanalysis with high statistical significance. Cooling in the east is associated with negative trends in the net heat flux from the atmosphere and enhanced equatorial upwelling related to a strengthening of the subtropical cells. Negative trends in the net heat flux also occur in the western tropical Pacific, but advective warming associated with a strengthening and shoaling of the equatorial undercurrent overwhelms these negative trends. The strengthening of the equatorial undercurrent is consistent with enhanced easterly wind stress, which is applied to the ocean reanalyses, and differential sea level trends that enhance the negative zonal height gradient across the Pacific. The Pacific North Equatorial countercurrent is also strengthening in all 4 reanalyses in association with a strengthening of the sea level trough at 10°N in the central and eastern Pacific. All 4 ocean reanalyses produce warming of 0.1-0.3 K/decade in the North Atlantic with statistical significance levels ranging from below 90-99%. The Atlantic is similar to the Pacific in having the equatorial undercurrent strengthening, but indications of shoaling are less consistent in the reanalyses and the North Equatorial Countercurrent in the Atlantic is not strengthening. Large-scale ocean mixed layer warming trends in the Indian Ocean in the reanalyses are interrupted by some regional cooling close to the equator. Net surface heat flux trends

Deglacial Tropical Atlantic subsurface warming links ocean circulation variability to the West African Monsoon.

PubMed

Schmidt, Matthew W; Chang, Ping; Parker, Andrew O; Ji, Link; He, Feng

2017-11-13

Multiple lines of evidence show that cold stadials in the North Atlantic were accompanied by both reductions in Atlantic Meridional Overturning Circulation (AMOC) and collapses of the West African Monsoon (WAM). Although records of terrestrial change identify abrupt WAM variability across the deglaciation, few studies show how ocean temperatures evolved across the deglaciation. To identify the mechanism linking AMOC to the WAM, we generated a new record of subsurface temperature variability over the last 21 kyr based on Mg/Ca ratios in a sub-thermocline dwelling planktonic foraminifera in an Eastern Equatorial Atlantic (EEA) sediment core from the Niger Delta. Our subsurface temperature record shows abrupt subsurface warming during both the Younger Dryas (YD) and Heinrich Event 1. We also conducted a new transient coupled ocean-atmosphere model simulation across the YD that better resolves the western boundary current dynamics and find a strong negative correlation between AMOC strength and EEA subsurface temperatures caused by changes in ocean circulation and rainfall responses that are consistent with the observed WAM change. Our combined proxy and modeling results provide the first evidence that an oceanic teleconnection between AMOC strength and subsurface temperature in the EEA impacted the intensity of the WAM on millennial time scales.

Gas exchange and CO2 flux in the tropical Atlantic Ocean determined from Rn-222 and pCO2 measurements

NASA Technical Reports Server (NTRS)

Smethie, W. M., Jr.; Takahashi, T.; Chipman, D. W.; Ledwell, J. R.

1985-01-01

The piston velocity for the tropical Atlantic Ocean has been determined from 29 radon profiles measured during the TTO Tropical Atlantic Study. By combining these data with the pCO2 data measured in the surface water and air samples, the net flux of CO2 across the sea-air interface has been calculated for the tropical Atlantic. The dependence of the piston velocity on wind speed is discussed, and possible causes for the high sea-to-air CO2 flux observed in the equatorial zone are examined.

Equatorial Indian Ocean subsurface current variability in an Ocean General Circulation Model

NASA Astrophysics Data System (ADS)

Gnanaseelan, C.; Deshpande, Aditi

2018-03-01

The variability of subsurface currents in the equatorial Indian Ocean is studied using high resolution Ocean General Circulation Model (OGCM) simulations during 1958-2009. February-March eastward equatorial subsurface current (ESC) shows weak variability whereas strong variability is observed in northern summer and fall ESC. An eastward subsurface current with maximum amplitude in the pycnocline is prominent right from summer to winter during strong Indian Ocean Dipole (IOD) years when air-sea coupling is significant. On the other hand during weak IOD years, both the air-sea coupling and the ESC are weak. This strongly suggests the role of ESC on the strength of IOD. The extension of the ESC to the summer months during the strong IOD years strengthens the oceanic response and supports intensification and maintenance of IODs through modulation of air sea coupling. Although the ESC is triggered by equatorial winds, the coupled air-sea interaction associated with IODs strengthens the ESC to persist for several seasons thereby establishing a positive feedback cycle with the surface. This suggests that the ESC plays a significant role in the coupled processes associated with the evolution and intensification of IOD events by cooling the eastern basin and strengthening thermocline-SST (sea surface temperature) interaction. As the impact of IOD events on Indian summer monsoon is significant only during strong IOD years, understanding and monitoring the evolution of ESC during these years is important for summer monsoon forecasting purposes. There is a westward phase propagation of anomalous subsurface currents which persists for a year during strong IOD years, whereas such persistence or phase propagation is not seen during weak IOD years, supporting the close association between ESC and strength of air sea coupling during strong IOD years. In this study we report the processes which strengthen the IOD events and the air sea coupling associated with IOD. It also unravels

Organic matter in eolian dusts over the Atlantic Ocean

NASA Technical Reports Server (NTRS)

Simoneit, B. R. T.

1977-01-01

The elemental and mineralogical composition and the microfossil and detritus content of particulate fallout from the lower troposphere over the Atlantic Ocean have been extensively documented in earlier work, and it was possible to ascribe terrigenous source areas to such fallout. A brief review of the organic geochemistry of eolian dusts is also presented here. The lipids of eolian dusts sampled from the air mass over the eastern Atlantic from about 35 deg N to 30 deg S were analyzed here. These lipids consisted mainly of normal alkanes, carboxylic acids and alcohols. The n-alkanes were found to range from n-C23 to n-C35 with high CPI values and maximizing at n-C27 in the North Atlantic, at n-C29 in the equatorial Atlantic and at n-C31 in the South Atlantic. The n-fatty acids had mostly bimodal distributions, ranging from n-C12 to n-C30 (high CPI), with maxima at n-C16 and in the northern samples at n-C24 and in the southern samples at n-C26. The n-alcohols ranged from n-C12 to n-C32, with high CPI values and maxima mainly at n-C28. The compositions of these lipids indicated that their terrigenous sources were comprised mainly of higher plant vegetation and desiccated lacustrine mud flats on the African continent.

Land-atmosphere-ocean interactions in the southeastern Atlantic: interannual variability

NASA Astrophysics Data System (ADS)

Sun, Xiaoming; Vizy, Edward K.; Cook, Kerry H.

2018-02-01

Land-atmosphere-ocean interactions in the southeastern South Atlantic and their connections to interannual variability are examined using a regional climate model coupled with an intermediate-level ocean model. In austral summer, zonal displacements of the South Atlantic subtropical high (SASH) can induce variations of mixed-layer currents in the Benguela upwelling region through surface wind stress curl anomalies near the Namibian coast, and an eastward shifted SASH is related to the first Pacific-South American mode. When the SASH is meridionally displaced, mixed layer vertically-integrated Ekman transport anomalies are mainly a response to the change of alongshore surface wind stress. The latitudinal shift of the SASH tends to dampen the anomalous alongshore wind by modulating the land-sea thermal contrast, while opposed by oceanic diffusion. Although the position of the SASH is closely linked to the phase of El Niño-Southern Oscillation (ENSO) and the southern annular mode (SAM) in austral summer, an overall relationship between Benguela upwelling strength and ENSO or SAM is absent. During austral winter, variations of the mixed layer Ekman transport in the Benguela upwelling region are connected to the strength of the SASH through its impact on both coastal wind stress curl and alongshore surface wind stress. Compared with austral summer, low-level cloud cover change plays a more important role. Although wintertime sea surface temperature fluctuations in the equatorial Atlantic are strong and may act to influence variability over the northern Benguela area, the surface heat budget analysis suggests that local air-sea interactions dominate.

Oxygen minimum zones in the eastern tropical Atlantic and Pacific oceans

NASA Astrophysics Data System (ADS)

Karstensen, Johannes; Stramma, Lothar; Visbeck, Martin

2008-06-01

corresponds well to the average oxygen ages for the well ventilated waters. However, in the density ranges of the suboxic OMZs the turn-over time substantially increases. This indicates that reduced ventilation in the outcrop is directly related to the existence of suboxic OMZs, but they are not obviously related to enhanced consumption indicated by the oxygen ages. The turn-over time suggests that the lower thermocline of the North Atlantic would be suboxic but at present this is compensated by the import of water from the well ventilated South Atlantic. The turn-over time approach itself is independent of details of ocean transport pathways. Instead the geographical location of the OMZ is to first order determined by: (i) the patterns of upwelling, either through Ekman or equatorial divergence, (ii) the regions of general sluggish horizontal transport at the eastern boundaries, and (iii) to a lesser extent to regions with high productivity as indicated through ocean colour data.

Decadal change of the south Atlantic ocean Angola-Benguela frontal zone since 1980

NASA Astrophysics Data System (ADS)

Vizy, Edward K.; Cook, Kerry H.; Sun, Xiaoming

2018-01-01

High-resolution simulations with a regional atmospheric model coupled to an intermediate-level mixed layer ocean model along with multiple atmospheric and oceanic reanalyses are analyzed to understand how and why the Angola-Benguela frontal Zone (ABFZ) has changed since 1980. A southward shift of 0.05°-0.55° latitude decade-1 in the annual mean ABFZ position accompanied by an intensification of + 0.05 to + 0.13 K/100-km decade-1 has occurred as ocean mixed layer temperatures have warmed (cooled) equatorward (poleward) of the front over the 1980-2014 period. These changes are captured in a 35-year model integration. The oceanic warming north of the ABFZ is associated with a weakening of vertical entrainment, reduced cooling associated with vertical diffusion, and a deepening of the mixed layer along the Angola coast. These changes coincide with a steady weakening of the onshore atmospheric flow as the zonal pressure gradient between the eastern equatorial Atlantic and the Congo Basin weakens. Oceanic cooling poleward of the ABFZ is primarily due to enhanced advection of cooler water from the south and east, increased cooling by vertical diffusion, and shoaling of the mixed layer depth. In the atmosphere, these changes are related to an intensification and poleward shift of the South Atlantic sub-tropical anticyclone as surface winds, hence the westward mixed layer ocean currents, intensify in the Benguela upwelling region along the Namibian coast. With a few caveats, these findings demonstrate that air/sea interactions play a prominent role in influencing the observed decadal variability of the ABFZ over the southeastern Atlantic since 1980.

78 FR 32556 - Safety Zone; 2013 Ocean City Air Show, Atlantic Ocean; Ocean City, MD

Federal Register 2010, 2011, 2012, 2013, 2014

2013-05-31

...-AA00 Safety Zone; 2013 Ocean City Air Show, Atlantic Ocean; Ocean City, MD AGENCY: Coast Guard, DHS... navigable waters of the Atlantic Ocean in the vicinity of Ocean City, MD to support the Ocean City Air Show... June 9, 2013, Ocean City, MD will host an air show event between Talbot Street and 33rd Street over the...

77 FR 22523 - Safety Zone; 2012 Ocean City Air Show; Atlantic Ocean, Ocean City, MD

Federal Register 2010, 2011, 2012, 2013, 2014

2012-04-16

...-AA00 Safety Zone; 2012 Ocean City Air Show; Atlantic Ocean, Ocean City, MD AGENCY: Coast Guard, DHS... the navigable waters of the Atlantic Ocean in Ocean City, MD. This action is necessary to provide for the safety of life on navigable waters during the 2012 Ocean City Air Show. This action is intended to...

Oligocene-Miocene magnetic stratigraphy carried by biogenic magnetite at sites U1334 and U1335 (equatorial Pacific Ocean)

NASA Astrophysics Data System (ADS)

Channell, J. E. T.; Ohneiser, C.; Yamamoto, Y.; Kesler, M. S.

2013-02-01