Antarctic bottom water in the Scotia Sea and the Drake Passage

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.

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

Biogeosciences ◽

10.5194/bg-11-651-2014 ◽

2014 ◽

Vol 11 (3) ◽

pp. 651-669 ◽

Cited By ~ 30

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.

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Circumpolar bottom water in the Scotia Sea and the Drake Passage

Oceanology ◽

10.1134/s0001437010010017 ◽

2010 ◽

Vol 50 (1) ◽

pp. 1-17 ◽

Cited By ~ 2

Author(s):

R. Yu. Tarakanov

Keyword(s):

Bottom Water ◽

Drake Passage ◽

Scotia Sea

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Ventilation of the abyss in the Atlantic sector of the Southern Ocean

Scientific Reports ◽

10.1038/s41598-021-86043-2 ◽

2021 ◽

Vol 11 (1) ◽

Author(s):

Camille Hayatte Akhoudas ◽

Jean-Baptiste Sallée ◽

F. Alexander Haumann ◽

Michael P. Meredith ◽

Alberto Naveira Garabato ◽

...

Keyword(s):

Southern Ocean ◽

Bottom Water ◽

Climate Models ◽

Deep Ocean ◽

Analytical Framework ◽

Weddell Sea ◽

Global Ocean ◽

Shelf Water ◽

Antarctic Bottom Water ◽

Atlantic Sector

AbstractThe Atlantic sector of the Southern Ocean is the world’s main production site of Antarctic Bottom Water, a water-mass that is ventilated at the ocean surface before sinking and entraining older water-masses—ultimately replenishing the abyssal global ocean. In recent decades, numerous attempts at estimating the rates of ventilation and overturning of Antarctic Bottom Water in this region have led to a strikingly broad range of results, with water transport-based calculations (8.4–9.7 Sv) yielding larger rates than tracer-based estimates (3.7–4.9 Sv). Here, we reconcile these conflicting views by integrating transport- and tracer-based estimates within a common analytical framework, in which bottom water formation processes are explicitly quantified. We show that the layer of Antarctic Bottom Water denser than 28.36 kg m$$^{-3}$$ - 3 $$\gamma _{n}$$ γ n is exported northward at a rate of 8.4 ± 0.7 Sv, composed of 4.5 ± 0.3 Sv of well-ventilated Dense Shelf Water, and 3.9 ± 0.5 Sv of old Circumpolar Deep Water entrained into cascading plumes. The majority, but not all, of the Dense Shelf Water (3.4 ± 0.6 Sv) is generated on the continental shelves of the Weddell Sea. Only 55% of AABW exported from the region is well ventilated and thus draws down heat and carbon into the deep ocean. Our findings unify traditionally contrasting views of Antarctic Bottom Water production in the Atlantic sector, and define a baseline, process-discerning target for its realistic representation in climate models.

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