Drake Passage

Lide, D, (Editor) CRC Handbook of Chemistry and 84th Edition - A Ready Book of Chemical Reference and Physical Data, CRC Press, LLC.. Boca Raton, FL, 2003. Lngmair, GW. et al. Samarium-146 in the Early Solar System Evidence from Neodymium in the Allende Meteorite, Science, 222, 1015-1017 (1983). Piepgras, D J. and G.J. Wasserburg Isotopic Composition of Neodymium in Waters from the Drake Passage/ Science, 217, 207-214 (1982). 

Figure 4.13. Elements of the global water balance with the role of the ocean taken into account. Notations wA0L, wA0P, wA0I, wA0P precipitation Hpo, Hop Straits of Gibraltar Rp, Rj, RL rivers EPA, E1A, EPA, ELA evaporation Apl, A1P the Antarctic Current MP1 the Cape Igolny Current CPj the East-Australian Current fiPL Bering Strait 1LP Arctic ice DPP Drake Passage IP Antarctic ice NPI Indonesian seas Slf> Sfl straits.

Figure 1 gives an overview of the cruise tracks and the DMS sampling stations in the Drake Passage and in Bransfield Strait. The land base in Antarctica was Palmer Station on Anvers Island. Most of the measurements were made in open ocean areas (Drake Passage) and in the inshore areas of Gerlache Strait. 

Ten-day isobaric back-trajectories were calculated for each day of the cruise (Harris, J., personal communication, 1986) indicating that air masses were predominantly advected from the open South Pacific Ocean. Wind velocities over the Drake Passage ranged between 3-30 m s 1, whereas in the inshore areas they never exceeded 10 m s 1. During about 70% of the cruise period the weather was characterized by overcast conditions with occasional snowfall and fog episodes. A high pressure weather situation occurred between April 8-14 which was responsible for sustained cloud-free conditions with intense daylight during this short period. Surface seawater temperatures were typically around 8°C in the Subantarctic and 2°C in the Antarctic and inshore waters, whereas air temperatures were around -0.S°C and showed much less latitudinal difference. 

Figure 1. Overview of the cruise track in the study area and DMS sampling locations in the Drake Passage and in Bransfield Strait. Cruise legs in the Drake Passage (1986) I, March 21-24, II, March 28-29, in, March 30-31 IV, April 24-27 Circles indicate stations including both air and seawater samples, triangles seawater samples only, squares air samples only, and hatched areas represent multiple adjacent stations where air and/or seawater samples were taken. (Reprinted with permission from Ref. 12. Copyright 1987 by the American Geophysical Union).

The sea-to-air flux of DMS in the study area was calculated to be about 4.4 /imol m 2d 1 over the open ocean (Drake Passage) and about 1.2 /imol m d 1 from the inshore waters of Gerlache and Bransfield Strait (121. The calculations were based on a simple parameterization of the stagnant film model (22). The results are estimated to be uncertain by a factor of 2 (1). The difference between the open ocean and inshore area values can be attributed mainly to differences in wind velocities rather than sea surface temperatures or aqueous DMS concentrations between both regions. 

In contrast to N, surprisingly little information is available on export rates of Fe from the surface ocean, despite the obvious importance of this parameter to biogeochem-ical models. Partly, this is due to the difficulties associated with making trace-metal clean measurements of sinking fluxes out of the mixed layer. Two published estimates from relatively nearshore waters present quite high export estimates of 2 pmol m day (in the Drake Passage, Martin et ai, 1990) and <10—140 pmol m day (in the Baltic Sea, Pohl et ai, 2004). 

Wefer G., Suess E., Balzer W., Eiebezeit G., Muller P. J., Ungerer C. A., and Zenk W. (1982) Fluxes of biogenic components from sediment trap deployment incircumpolar waters of the Drake Passage. Nature 299, 145-147. 

Figure 5 Representative depth profiles of Nd-isotope ratios from the North Atlantic and Pacific oceans and the Drake Passage. The Atlantic and Pacific profiles were chosen to encompass the range of values for deep water in those oceans. Symbols show the data. The diagram illustrates the differences between the oceans and the greater variability of Nd isotopes in shallow versus deep waters (sources Piepgras and Wasserburg, 1982, 1983, 1987 Spivack and Wasserburg, 1988 Piepgras and Jacobsen, 1988 Shimizu et al., 1994).

The limited seawater data from the circum-Antarctic display uniform neodymium-isotope ratios intermediate to the Atlantic and Pacihc (sNd = 8 to —9). The only neodymium-isotope data available are from two profiles in the Drake Passage and one in the eastern Pacific sector (Piepgras and Wasserburg, 1982). 

Passage values (Figure 7). This may indicate a source of neodymium with high isotope ratios in the South Atlantic. However, it is premature to conclude that deep South Atlantic neodymium-isotope ratios overstep the Southern Ocean values, for the following reasons. The maxima for all of the deep South Atlantic waters are between SNd = 7 to —9, more variable than presently available data from the Drake Passage but still quite similar. This range is also similar to circumpolar Fe-Mn sediments (Albare(c)de et al., 1997). Depth profiles from the western Indian Ocean near southern Africa are similar to the South Atlantic and Drake Passage, but like the South... 

Figure 11 Nd-isotope ratios versus silicate in Pacific, Indian, and Southern Ocean deep waters. The positive correlation shows that Nd-isotope ratios trace mixing of deep waters from the circum-Antarctic and Pacific. Plotted data are from >2,500 mb si, except two Drake Passage data from 1,900 m and 2,000 m (Nd data sources Piepgras and Wasserburg, 1980, 1982 Piepgras and Jacobsen, 1988 Bertram and Elderfield, 1993 Shimizu et al., 1994 Jeandel et al., 1998). Where salinity or silicate were not available in the publication, they were estimated from Levitus...

Piepgras D. J. and Wasserburg G. J. (1982) Isotopic composition of neodymium in waters from the Drake Passage. Science 217(4556), 207-214. 

Toggweiler J. R. and Samuels B. (1995) Effect of Drake Passage on the global thermohaline circulation. Deep-Sea... 

Another experiment carried out by Martin et al. in the Atlantic sector of the Southern Ocean showed that the highly productive neritic Gerlache Strait waters have an abundance of Fe (7.4 nM) which facilitates phytoplankton blooming and major nutrient removal (133). The results of the investigation carried out in low productivity offshore Drake Passage waters showed low levels of dissolved Fe (0.16 nM -, the concentration was so low that the phytoplankton was able to use less than 10% of the major nutrient available to them. 

Herb, R. 1971. Distribution of Recent benthonic foraminifera in the Drake Passage. In Llano, G. A. Wallen, I. E. (eds) Biology of Antarctic Seas IV. Antarctic Research Series, 17. American Geophysical Union, Washington DC, 251-300. 

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