Guy Williams, ACE CRC
IMAS Sandy Bay seminar room
Wednesday 21st December, 13:00 – 13:50
Abstract:
New oceanographic data from instrumented marine mammals have been addressing critical spatial and temporal gaps in our understanding of the polar ocean, in particular south of the continental shelf break in the coastal polynya regions that form dense shelf water for Antarctic Bottom Water (AABW) production. In 2010 southern elephant seals (Mirounga leonina), fitted with Conductivity-Temperature-Depth sensors and deployed from Macquarie Island collected unique observations in the Adélie Depression (142-145 °E). A two-month occupation of the upper 300m in Commonwealth Bay from March through April described for the first time the pre-conditioning of the new winter mixed layer after the onset of sea ice formation.
In 2011, elephant seals from Davis Station and Kerguelen Island did even better, for longer, this time over the Prydz Bay/Cape Darnley continental shelf and slope region (65-80 °E) from February to October. Historically this eastern sector of the Weddell-Enderby Basin (60-70 °E) was identified as having a local source of AABW, but it was largely ignored until recent satellite analyses found that the Cape Darnley polynya had the 2nd highest sea ice production around Antarctica. This led to an ongoing Japanese program of moored instruments that has documented seasonal overflows of modified shelf water in the canyons north/north west of Cape Darnley. An open question remained as to the whether Cape Darnley is the source of these overflows, or Prydz Bay to the east, or both. The 2011 elephant seal data has confirmed not only the presence of very High Salinity Shelf water west of Cape Darnley (up to 34.9), relative to dense shelf water from the Prydz Bay region, but has also captured very rare CTD observations of the modified shelf water overflows to depths of ~1700m in wintertime. These clearly show an increase in bottom salinity west of 69°E and the dominance of the Cape Darnley polynya in this dual-source (Cape Darnley/Prydz Bay) AABW production system.
This talk will present these results and showcase other unique insights from the elephant seal data in this region including i) summer-fall transects across the front of the Amery Ice Shelf, ii) sea ice growth rates from March through June and iii) the seasonal variability in the upper ocean from 50—70 °S from monthly meridional transects between February and July. It is difficult to overestimate the value of this dataset relative to traditional ship-based surveys and so there is a strong case for the ongoing deployment of these instruments for the long-term monitoring of this sector of the Southern Ocean between 50—70 °S, 60-90 °E.