Water masses and currents of the Southern Ocean at the Greenwich Meridian

Tides have a large impact on coastal polynyas around Antarctica. We investigate the effect of semi-diurnal tidal cycles on the seawater carbonate chemistry in a coastal polynya hugging the Ekstr&#246;m Ice Shelf in the south-eastern Weddell Sea. This region experiences some of the strongest tides in the Southern Ocean. We assess the implications for the contribution of coastal polynyas to the carbon dioxide (CO2) air-sea flux of the Weddell Sea.Two site visits, in January 2015 and January 2019, are intercompared in terms of the dissolved inorganic carbon (DIC) concentration, total alkalinity, pH, and CO2 partial pressure (pCO2). The tides induce large variability in the carbonate chemistry of the coastal polynya in the austral summer: DIC concentrations vary between 2174 and 2223 umol kg-1.The tidal fluctuation in the DIC concentration can swing the polynya from a sink to a source of atmospheric CO2 on a semi-diurnal timescale. We attribute these changes to the mixing of different water masses. The amount of variability induced by tides depends on &#8211; and is associated with &#8211; large scale oceanographic and biogeochemical processes that affect the characteristics and presence of the water masses being mixed, such as the rate of sea ice melt.Sampling strategies in Antarctic coastal polynyas should always take tidal influences into account. This would help to reduce biases in our understanding of how coastal polynyas contribute to the CO2 uptake by the Southern Ocean.

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Influence of different water masses and biological activity on dimethylsulphide and dimethylsulphoniopropionate in the subantarctic zone of the Southern Ocean during ACE 1

Journal of Geophysical Research Atmospheres ◽

10.1029/98jd01200 ◽

1998 ◽

Vol 103 (D13) ◽

pp. 16691-16701 ◽

Cited By ~ 43

Author(s):

Graham B. Jones ◽

Mark A. J. Curran ◽

Hilton B. Swan ◽

Richard M. Greene ◽

F. Brian Griffiths ◽

...

Keyword(s):

Biological Activity ◽

Southern Ocean ◽

Water Masses

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Water Masses and their Properties at 160°W in the Southern Ocean

Journal of Engineering Physics and Thermophysics ◽

10.5928/kaiyou1942.24.21 ◽

1968 ◽

Vol 24 (1) ◽

pp. 21-31 ◽

Cited By ~ 10

Author(s):

Ricardo M. PYTKOWICZ

Keyword(s):

Southern Ocean ◽

Water Masses

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Middle Holocene expansion of Pacific Deep Water into the Southern Ocean

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1908138117 ◽

2019 ◽

Vol 117 (2) ◽

pp. 889-894

Author(s):

Torben Struve ◽

David J. Wilson ◽

Tina van de Flierdt ◽

Naomi Pratt ◽

Kirsty C. Crocket

Keyword(s):

Southern Ocean ◽

Ocean Circulation ◽

Deep Water ◽

Water Masses ◽

Ocean Dynamics ◽

Global Ocean ◽

Circulation System ◽

The Holocene ◽

Middle Holocene ◽

Deep Mixing

The Southern Ocean is a key region for the overturning and mixing of water masses within the global ocean circulation system. Because Southern Ocean dynamics are influenced by the Southern Hemisphere westerly winds (SWW), changes in the westerly wind forcing could significantly affect the circulation and mixing of water masses in this important location. While changes in SWW forcing during the Holocene (i.e., the last ∼11,700 y) have been documented, evidence of the oceanic response to these changes is equivocal. Here we use the neodymium (Nd) isotopic composition of absolute-dated cold-water coral skeletons to show that there have been distinct changes in the chemistry of the Southern Ocean water column during the Holocene. Our results reveal a pronounced Middle Holocene excursion (peaking ∼7,000–6,000 y before present), at the depth level presently occupied by Upper Circumpolar Deep Water (UCDW), toward Nd isotope values more typical of Pacific waters. We suggest that poleward-reduced SWW forcing during the Middle Holocene led to both reduced Southern Ocean deep mixing and enhanced influx of Pacific Deep Water into UCDW, inducing a water mass structure that was significantly different from today. Poleward SWW intensification during the Late Holocene could then have reinforced deep mixing along and across density surfaces, thus enhancing the release of accumulated CO2 to the atmosphere.

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