First Advisor

Suzanne Estes

Date of Award


Document Type


Degree Name

Bachelor of Science (B.S.) in Environmental Science and University Honors


Environmental Science and Management


Bottom water (Oceanography) -- Indian Ocean, Ocean circulation -- Indian Ocean




A recognizable warming and freshening of Antarctic Bottom Water (AABW) throughout much of the Southern Ocean is one of the major findings of the international long-line hydrographic programs of 1990’s and the 2000's. A 2016 GO-SHIP repeat of the I08S line (80-90ºE) in the southeast Indian Ocean found continued, but weaker, AABW warming and significantly stronger freshening in the Antarctic-Australian Basin (A-AB). It has been proposed that the 2010 B9b iceberg calving along the Adélie Land Coast may be linked to this pronounced freshening. The present study seeks to affirm or challenge this hypothesis through a quantitative investigation into the origins of A-AB (i.e. I08S) bottom water. A water mass fraction mixing analysis is used to determine a) the contribution of individual formation regions to the bottom water seen at I08S, and b) how these contributions may have changed since the first occupation of the line. Long-term mean source water properties point to Adélie Bottom Water (ADLBW) as the sole dominant source of A-AB AABW. However, employing source water properties from times preceding each occupation I08S (1994, 2007, 2016), suggests that prior to 2007, Ross Sea Bottom Water (RSBW) was the dominant source (61% and 75%, respectively) and after 2007 there was a shift in composition (ADLBW 44%, RSBW 34%). This result suggests that it is feasible that the B9b calving that impacted ADLBW formation is, at least, partially responsible for changes seen at I08S. Nevertheless, given that there are significant contributions from sources, it seems unlikely that this single event is the sole driver of the observed freshening. A CFC age analysis of both source and I08S bottom waters confirms the estimated timescales to within +/- 5 years.


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