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[MIS15-05] Source waters of Antarctic Bottom Water observed in the east Weddell-Enderby Basin (55°E)
Keywords:Weddell-Enderby Basin, Antarctic Bottom Water
We estimated the composition of Antarctic Bottom Water (neutral density γ > 1028.27 kg/m3) in the eastern Weddell-Enderby basin by using the data from R/V Mirai along GO-SHIP section I07S (55° E longitude from 30° S to 65° S) and from R/V Hakuho off Cape Darnley from 2018 to 2020.
While it is possible that bottom waters from far east (the Ross Sea and off Adelie Coast) can arrive through the Princess Elizabeth Trough, the temperature-salinity relation in our data shows that the bottom water at γ > 1028.34 kg/m3 is not affected by the eastern water masses. Results from numerical simulations and other water mass analyses suggest that even in the lighter layers ( γ < 1028.34 kg/m3 ) the contribution from the eastern water masses are negligible. We therefore assumed that AABW at 55° E is a mixture of Weddell Sea Deep Water (WSDW), Cape Darnley Bottom Water (CDBW), southern Lower Circumpolar Deep Water (LCDW-S) and northern Lower Circumpolar Deep Water (LCDW-N). We applied a least squares fit with non-negative constraint to six conserved quantities, namely, mass, temperature, salinity, and three quasi-tracers which are combination of phosphpate, nitrate, and silicate with dissolved oxygen at the Redfield ratios. By purturbing the source water mass properties, we esimated uncertainty of the composition.
The result shows that at the upper AABW (γ = 1028.27 kg/m3 ), CDBW = 0 ― 20 %, WSDW = 5 ― 35 %, LCDW-S + LCDW-N = 70 ― 95% and that at the lower AABW ( γ =1028.35 kg/m3 ), CDBW = 0 ― 35%, WSDW = 35 ― 75 %, LCDW-S + LCDW-N = 25 ― 45 %. The composition suggests that the clockwise general circulation of the deep Weddell-Enderby basin carries WSDW and explains the dominance of this water mass. Closer to the coast, however, we find a similar contribution from CDBW.
While it is possible that bottom waters from far east (the Ross Sea and off Adelie Coast) can arrive through the Princess Elizabeth Trough, the temperature-salinity relation in our data shows that the bottom water at γ > 1028.34 kg/m3 is not affected by the eastern water masses. Results from numerical simulations and other water mass analyses suggest that even in the lighter layers ( γ < 1028.34 kg/m3 ) the contribution from the eastern water masses are negligible. We therefore assumed that AABW at 55° E is a mixture of Weddell Sea Deep Water (WSDW), Cape Darnley Bottom Water (CDBW), southern Lower Circumpolar Deep Water (LCDW-S) and northern Lower Circumpolar Deep Water (LCDW-N). We applied a least squares fit with non-negative constraint to six conserved quantities, namely, mass, temperature, salinity, and three quasi-tracers which are combination of phosphpate, nitrate, and silicate with dissolved oxygen at the Redfield ratios. By purturbing the source water mass properties, we esimated uncertainty of the composition.
The result shows that at the upper AABW (γ = 1028.27 kg/m3 ), CDBW = 0 ― 20 %, WSDW = 5 ― 35 %, LCDW-S + LCDW-N = 70 ― 95% and that at the lower AABW ( γ =1028.35 kg/m3 ), CDBW = 0 ― 35%, WSDW = 35 ― 75 %, LCDW-S + LCDW-N = 25 ― 45 %. The composition suggests that the clockwise general circulation of the deep Weddell-Enderby basin carries WSDW and explains the dominance of this water mass. Closer to the coast, however, we find a similar contribution from CDBW.