scholarly journals Dissolved Fe across the Weddell Sea and Drake Passage: impact of DFe on nutrients uptake in the Weddell Sea

2013 ◽  
Vol 10 (4) ◽  
pp. 7433-7489 ◽  
Author(s):  
M. B. Klunder ◽  
P. Laan ◽  
H. J. W. De Baar ◽  
I. Neven ◽  
R. Middag ◽  
...  
Keyword(s):  
Deep Water ◽  
Bottom Water ◽  
Drake Passage ◽  
Weddell Sea ◽  
Dust Deposition ◽  
Scotia Sea ◽  
Ice Melt ◽  
Sea Bottom ◽  
Poc Export ◽  
Bottom Waters

Abstract. This manuscript reports the first full depth distributions of dissolved iron (DFe) over a high resolution Weddell Sea and Drake Passage transect. Very low dissolved DFe concentrations (0.01–0.1 nM range) were observed in the surface waters in the Weddell Sea, and within the Polar regime in the Drake Passage. Locally, enrichment in surface DFe was observed, likely due to recent ice melt (Weddell Sea) or dust deposition (Drake Passage). In the Weddell Sea, the low DFe concentrations can be partly explained by high POC export and/or primary production (indicated by chlorophyll fluorescence). As expected, in high DFe regions a strong silicate drawdown compared to nitrate drawdown was observed. However, this difference in drawdown between these nutrients appears not related to biological activity on the Peninsula shelf. In the Western Weddell Sea transect, with relatively small diatoms, no relationship between N:P and N:Si removal ratios and DFe was observed. For comparison, nutrient depletion is also presented for a transect along the Greenwich Meridian (Klunder et al., 2011), where diatoms are significantly larger, the N:P and N:Si removal ratio increased with increasing DFe. These findings confirm the important role of DFe in Southern Ocean (biologically mediated) nutrient cycles. Over the shelf around the Antarctic Peninsula, higher DFe concentrations (> 1.5 nM) were observed. These elevated concentrations of Fe were transported into Drake Passage along isopycnal surfaces. At the South American continent, high (> 2 nM) DFe concentrations were caused by fluvial/glacial input of DFe. On the Weddell Sea side of the Peninsula region, formation of deep water (by downslope convection) caused relatively high Fe (0.6–0.8 nM) concentrations in the bottom waters relative to the water masses at mid depth (0.2–0.4 nM). During transit of Weddell Sea Bottom Water to Drake Passage, through the Scotia Sea, extra DFe is taken up from seafloor sources, resulting in highest bottom water concentrations in the southernmost part of the Drake Passage of > 1 nM. The Weddell Sea Deep Water concentrations (~ 0.32 nM) were consistent with the lowest DFe concentrations observed in Atlantic AABW.

scholarly journals Dissolved Fe across the Weddell Sea and Drake Passage: impact of DFe on nutrient uptake

2014 ◽  
Vol 11 (3) ◽  
pp. 651-669 ◽  
Author(s):  
M. B. Klunder ◽  
P. Laan ◽  
H. J. W. De Baar ◽  
R. Middag ◽  
I. Neven ◽  
...  
Keyword(s):  
Deep Water ◽  
Bottom Water ◽  
Drake Passage ◽  
Weddell Sea ◽  
Dust Deposition ◽  
Scotia Sea ◽  
Ice Melt ◽  
Sea Bottom ◽  
Phytoplankton Communities ◽  
The Difference

Abstract. This manuscript reports the first full depth distributions of dissolved iron (DFe) over a high-resolution Weddell Sea and Drake Passage transect. Very low dissolved DFe concentrations (0.01–0.1 nM range) were observed in the surface waters of the Weddell Sea, and within the Drake Passage polar regime. Locally, enrichment in surface DFe was observed, likely due to recent ice melt (Weddell Sea) or dust deposition (Drake Passage). As expected, in low DFe regions, usually a small silicate drawdown compared to the nitrate drawdown was observed. However, the difference in drawdown between these nutrients appeared not related to DFe availability in the western Weddell Sea. In this region with relatively small diatoms, no relationship between N : P and N : Si removal ratios and DFe was observed. In comparison, along the Greenwich Meridian (Klunder et al., 2011a), where diatoms are significantly larger, the N : P and N : Si removal ratios did increase with increasing DFe. These findings confirm the important role of DFe in biologically mediated nutrient cycles in the Southern Ocean and imply DFe availability might play a role in shaping phytoplankton communities and constraining cell sizes. Over the shelf around the Antarctic Peninsula, higher DFe concentrations (>1.5 nM) were observed. These elevated concentrations of Fe were transported into Drake Passage along isopycnal surfaces. Near the South American continent, high (>2 nM) DFe concentrations were caused by fluvial/glacial input of DFe. On the Weddell Sea side of the Peninsula region, formation of deep water (by downslope convection) caused relatively high Fe (0.6–0.8 nM) concentrations in the bottom waters relative to the water masses at mid-depth (0.2–0.4 nM). During transit of Weddell Sea Bottom Water to the Drake Passage, through the Scotia Sea, additional DFe is taken up from seafloor sources, resulting in highest bottom water concentrations in the southernmost part of the Drake Passage in excess of 1 nM. The Weddell Sea Deep Water concentrations (∼0.32 nM) were consistent with the lowest DFe concentrations observed in Antarctic bottom water in the Atlantic Ocean.

An east-west contrasting changes of Antarctic Bottom Water properties in the Southern Indian Ocean over the last three decades

2021 ◽  
Author(s):  
Yeon Choi ◽  
SungHyun Nam
Keyword(s):  
Indian Ocean ◽  
Deep Water ◽  
Bottom Water ◽  
Ross Sea ◽  
Weddell Sea ◽  
Southern Indian Ocean ◽  
Antarctic Bottom Water ◽  
Sea Bottom ◽  
East West ◽  
Source Waters

<p>Physical properties of Antarctic Bottom Water (AABW) derived from mixture of multiple source waters of different properties, are significantly affected by and contribute to the climate change. This study reveals a contrasting east-west pattern of changes in AABW temperature and salinity in the Southern Indian Ocean (SIO), which continues to become warmer (0.04 ± 0.01<sup></sup>°C/decade) and more saline (0.002 ± 0.001 kg/g/decade) in the western SIO whereas warmer (0.03 ± 0.01<sup></sup>°C/decade) and fresher (-0.004 ± 0.001 kg/g/decade) in the eastern SIO over the past three decades, based on repeat hydrographic observations along meridional lines (1993, 1996, 2008, and 2019 in the western SIO and 1995, 2004, and 2012 in the eastern SIO). Warming and salinification of AABW consisting of the Cape Darnley Bottom Water (CDBW), Weddell Sea Deep Water (WSDW), and Lower Circumpolar Deep Water (LCDW) in the western SIO, are explained by changing proportion of source waters during the period, e.g., decreasing portion of relatively fresh CDBW (from 68% to 59%), and increasing portions of saline WSDW (from 30% to 34%) and warm and saline LCDW (from 2% to 7%). In contrast, in the eastern SIO, warming and freshening of the AABW consisting of the Ross Sea Bottom Water (RSBW), Adélie Land Bottom Water (ALBW), and LCDW are not explained by the changing proportion but properties of the source waters during the period, e.g., warming and freshening of RSBW (0.08°C/decade and -0.013 kg/g/decade) and ALBW (0.01°C/decade and -0.008 kg/g/decade). The east-west contrasting changes of AABW properties (eastern freshening and western salinification) over the last three decades have important consequences within and beyond the SIO.</p>

scholarly journals Reversal of freshening trend of Antarctic Bottom Water in the Australian-Antarctic Basin during 2010s

2020 ◽  
Vol 10 (1) ◽  
Author(s):  
S. Aoki ◽  
K. Yamazaki ◽  
D. Hirano ◽  
K. Katsumata ◽  
K. Shimada ◽  
...  
Keyword(s):  
Continental Slope ◽  
Bottom Water ◽  
Ross Sea ◽  
Bottom Layer ◽  
Ice Shelves ◽  
West Antarctic ◽  
Sea Bottom ◽  
Salinity Increase ◽  
Bottom Waters ◽  
Late Twentieth

Abstract The Antarctic continental margin supplies the densest bottom water to the global abyss. From the late twentieth century, an acceleration in the long-term freshening of Antarctic Bottom Waters (AABW) has been detected in the Australian-Antarctic Basin. Our latest hydrographic observations reveal that, in the late 2010s, the freshening trend has reversed broadly over the continental slope. Near-bottom salinities in 2018–2019 were higher than during 2011–2015. Along 170° E, the salinity increase between 2011 and 2018 was greater than that observed in the west. The layer thickness of the densest AABW increased during the 2010s, suggesting that the Ross Sea Bottom Water intensification was a major source of the salinity increase. Freshwater content on the continental slope decreased at a rate of 58 ± 37 Gt/a in the near-bottom layer. The decadal change is very likely due to changes in Ross Sea shelf water attributable to a decrease in meltwater from West Antarctic ice shelves for the corresponding period.

scholarly journals The Skytrain plate and tectonic evolution of southwest Gondwana since Jurassic times

2020 ◽  
Vol 10 (1) ◽  
Author(s):  
Graeme Eagles ◽  
Hannes Eisermann
Keyword(s):  
Tectonic Evolution ◽  
Drake Passage ◽  
Weddell Sea ◽  
Falkland Islands ◽  
South American ◽  
Long Distance ◽  
Oblique Collision ◽  
Scotia Sea ◽  
Continental Extension ◽  
Pacific Margin

AbstractUncertainty about the structure of the Falkland Plateau Basin has long hindered understanding of tectonic evolution in southwest Gondwana. New aeromagnetic data from the basin reveal Jurassic-onset seafloor spreading by motion of a single newly-recognized plate, Skytrain, which also governed continental extension in the Weddell Sea Embayment and possibly further afield in Antarctica. The Skytrain plate resolves a nearly century-old controversy by requiring a South American setting for the Falkland Islands in Gondwana. The Skytrain plate’s later motion provides a unifying context for post-Cambrian wide-angle paleomagnetic rotation, Cretaceous uplift, and post-Permian oblique collision in the Ellsworth Mountains of Antarctica. Further north, the Skytrain plate’s margins built a continuous conjugate ocean to the Weddell Sea in the Falkland Plateau Basin and central Scotia Sea. This ocean rules out venerable correlation-based interpretations for a Pacific margin location and subsequent long-distance translation of the South Georgia microcontinent as the Drake Passage gateway opened.

scholarly journals Assessment of the structure and variability of Weddell Sea water masses in distinct ocean reanalysis products

Ocean Science ◽  
2014 ◽  
Vol 10 (3) ◽  
pp. 523-546 ◽  
Author(s):  
T. S. Dotto ◽  
R. Kerr ◽  
M. M. Mata ◽  
M. Azaneu ◽  
I. Wainer ◽  
...  
Keyword(s):  
Deep Water ◽  
Sea Water ◽  
Horizontal Resolution ◽  
Weddell Sea ◽  
Water Masses ◽  
Ocean Reanalysis ◽  
In Situ Data ◽  
Ocean Data Assimilation ◽  
Sea Bottom ◽  
Warm Deep Water

Abstract. We assessed and evaluated the performance of five ocean reanalysis products in reproducing essential hydrographic properties and their associated temporal variability for the Weddell Sea, Antarctica. The products used in this assessment were ECMWF ORAS4 (European Centre for Medium-Range Weather Forecasts Ocean Reanalysis System 4), CFSR (Climate Forecast System Reanalysis), MyOcean UR025.4 (University of Reading), ECCO2 (Estimating the Circulation and Climate of the Ocean, Phase II) and SODA (Simple Ocean Data Assimilation). The present study focuses on the Weddell Sea deep layer, which is composed of the following three main water masses: Warm Deep Water (WDW), Weddell Sea Deep Water (WSDW) and Weddell Sea Bottom Water (WSBW). The MyOcean UR025.4 product provided the most accurate representation of the structure and thermohaline properties of the Weddell Sea water masses when compared with observations. All the ocean reanalysis products analyzed exhibited limited capabilities in representing the surface water masses in the Weddell Sea. The CFSR and ECCO2 products were not able to represent deep water masses with a neutral density ≥ 28.40 kg m−3, which was considered the WSBW's upper limit throughout the simulation period. The expected WDW warming was only reproduced by the SODA product, whereas the ECCO2 product was able to represent the trends in the WSDW's hydrographic properties. All the assessed ocean reanalyses were able to represent the decrease in the WSBW's density, except the SODA product in the inner Weddell Sea. Improvements in parameterization may have as much impact on the reanalyses assessed as improvements in horizontal resolution primarily because the Southern Ocean lacks in situ data, and the data that are currently available are summer-biased. The choice of the reanalysis product should be made carefully, taking into account the performance, the parameters of interest, and the type of physical processes to be evaluated.

scholarly journals On the Seasonal Signal of the Filchner Overflow, Weddell Sea, Antarctica

2014 ◽  
Vol 44 (4) ◽  
pp. 1230-1243 ◽  
Author(s):  
E. Darelius ◽  
K. O. Strand ◽  
S. Østerhus ◽  
T. Gammeslrød ◽  
M. Årthun ◽  
...  
Keyword(s):  
Seasonal Variability ◽  
Weddell Sea ◽  
Shelf Water ◽  
Ice Shelf ◽  
Sea Bottom ◽  
Plume Region ◽  
Long Time ◽  
Seasonal Signals ◽  
Bottom Waters ◽  
Seasonal Signal

Abstract The cold ice shelf water (ISW) that formed below the Filchner–Ronne Ice Shelf in the southwestern Weddell Sea, Antarctica, escapes the ice shelf cavity through the Filchner Depression and spills over its sill at a rate of 1.6 Sverdrups (Sv; 1 Sv ≡ 106 m3 s−1), thus contributing significantly to the production of Weddell Sea Bottom Water. Here, the authors examine all available observational data from the region—including five year-long time series of mooring data from the Filchner sill—to examine the seasonal variability of the outflow. The temperature of the ISW outflow is found to vary seasonally by 0.07°C with a maximum in April. The accompanying signal in salinity causes a seasonal signal in density of 0.03–0.04 kg m−3, potentially changing the penetration depth of the ISW plume by more than 500 m. Contrary to recent modeling, the observations show no seasonal variability in outflow velocity. The seasonality observed at the sill is, at least partly, due to the admixture of high-salinity shelf water from the Berkner Bank. Observations and numerical modeling suggest, however, seasonal signals in the circulation upstream (i.e., in the ice shelf cavity and in the Filchner Depression) that—although processes and linkages are unclear—are likely to contribute to the seasonal signal observed at the sill. In the plume region downstream of the sill, the source variability is apparent only within the very densest portions of the ISW plume. In the more diluted part of the plume, the source variability is overcome by the seasonality in the properties of the water entrained at the shelf break. This will have implications for the properties of the generated bottom waters.

scholarly journals Benthic Foraminiferal Response to the Millennial-Scale Variations in Monsoon-Driven Productivity and Deep-Water Oxygenation in the Western Bay of Bengal During the Last 45 ka

2021 ◽  
Vol 8 ◽  
Author(s):  
Komal Verma ◽  
Harshit Singh ◽  
Arun Deo Singh ◽  
Pradyumna Singh ◽  
Rajeev Kumar Satpathy ◽  
...  
Keyword(s):  
Organic Matter ◽  
Deep Water ◽  
Sea Floor ◽  
The Core ◽  
Sea Bottom ◽  
Core Site ◽  
Bottom Waters ◽  
Western Bay Of Bengal ◽  
Matter Flux ◽  
Millennial Scale

In this study, we presented a high-resolution benthic foraminiferal assemblage record from the western Bay of Bengal (BoB) (off Krishna–Godavari Basin) showing millennial-scale variations during the last 45 ka. We studied temporal variations in benthic foraminiferal assemblages (relative abundances of ecologically sensitive groups/species, microhabitat categories, and morphogroups) to infer past changes in sea bottom environment and to understand how monsoon induced primary productivity-driven organic matter export flux and externally sourced deep-water masses impacted the deep-sea environment at the core site. Our records reveal a strong coupling between surface productivity and benthic environment on glacial/interglacial and millennial scale in concert with Northern Hemisphere climate events. Faunal data suggest a relatively oxic environment when the organic matter flux to the sea floor was low due to low primary production during intensified summer monsoon attributing surface water stratification and less nutrient availability in the mixed layer. Furthermore, records of oxygen-sensitive benthic taxa (low-oxygen vs. high-oxygen benthics) indicate that changes in deep-water circulation combined with the primary productivity-driven organic matter flux modulated the sea bottom oxygen condition over the last 45 ka. We suggest that the bottom water at the core site was well-ventilated during the Holocene (except for the period since 3 ka) compared with the late glacial period. At the millennial timescale, our faunal proxy records suggest relatively oxygen-poor condition at the sea floor during the intervals corresponding to the cold stadials and North Atlantic Heinrich events (H1, H2, H3, and H4) compared with the Dansgaard/Oeschger (D-O) warm interstadials. The study further reveals oxygen-poor bottom waters during the last glacial maximum (LGM, 19–22 ka) which is more pronounced during 21–22 ka. A major shift in sea bottom condition from an oxygenated bottom water during the warm Bølling–Allerød (B/A) (between 13 and 15 ka) to the oxygen-depleted condition during the cold Younger Dryas (YD) period (between 10.5 and 13 ka) is noticed. It is likely that the enhanced inflow of North Atlantic Deep Water (NADW) to BoB would have ventilated bottom waters at the core site during the Holocene, B/A event, and probably during the D-O interstadials of marine isotope stage (MIS) 3.

scholarly journals Water masses in the Atlantic Ocean: characteristics and distributions

Ocean Science ◽  
2021 ◽  
Vol 17 (2) ◽  
pp. 463-486
Author(s):  
Mian Liu ◽  
Toste Tanhua
Keyword(s):  
Atlantic Ocean ◽  
Deep Water ◽  
Bottom Water ◽  
Water Mass ◽  
Sea Water ◽  
Weddell Sea ◽  
Water Masses ◽  
Global Ocean ◽  
Intermediate Water ◽  
The North

Abstract. A large number of water masses are presented in the Atlantic Ocean, and knowledge of their distributions and properties is important for understanding and monitoring of a range of oceanographic phenomena. The characteristics and distributions of water masses in biogeochemical space are useful for, in particular, chemical and biological oceanography to understand the origin and mixing history of water samples. Here, we define the characteristics of the major water masses in the Atlantic Ocean as source water types (SWTs) from their formation areas, and map out their distributions. The SWTs are described by six properties taken from the biased-adjusted Global Ocean Data Analysis Project version 2 (GLODAPv2) data product, including both conservative (conservative temperature and absolute salinity) and non-conservative (oxygen, silicate, phosphate and nitrate) properties. The distributions of these water masses are investigated with the use of the optimum multi-parameter (OMP) method and mapped out. The Atlantic Ocean is divided into four vertical layers by distinct neutral densities and four zonal layers to guide the identification and characterization. The water masses in the upper layer originate from wintertime subduction and are defined as central waters. Below the upper layer, the intermediate layer consists of three main water masses: Antarctic Intermediate Water (AAIW), Subarctic Intermediate Water (SAIW) and Mediterranean Water (MW). The North Atlantic Deep Water (NADW, divided into its upper and lower components) is the dominating water mass in the deep and overflow layer. The origin of both the upper and lower NADW is the Labrador Sea Water (LSW), the Iceland–Scotland Overflow Water (ISOW) and the Denmark Strait Overflow Water (DSOW). The Antarctic Bottom Water (AABW) is the only natural water mass in the bottom layer, and this water mass is redefined as Northeast Atlantic Bottom Water (NEABW) in the north of the Equator due to the change of key properties, especially silicate. Similar with NADW, two additional water masses, Circumpolar Deep Water (CDW) and Weddell Sea Bottom Water (WSBW), are defined in the Weddell Sea region in order to understand the origin of AABW.

Sign in / Sign up

Export Citation Format

Share Document