S. Stammerjohn, PI
The western Antarctic Peninsula (WAP), inclusive of the PAL LTER study region, is one of the fastest changing regions on earth, with an annual warming 4 times the global rate since the early 1950’s (0.13 degC/decade globally versus 0.55 degC/decade WAP). The seasonality of sea ice shows similar rapid changes (figure below left): the autumn advance is occurring ~2 months later (over the last 32 years, 1979-2010) and the spring retreat ~1 month earlier, both resulting in a ~3-month shorter annual ice season. Decadal changes in monthly surface air temperature (figure below right) measured at several WAP stations (north-to-south) reveal pronounced winter warming over the last 3 decades, particularly mid-peninsula in the heart of the PAL study region, concurrent with the disappearance of perennial sea ice (in blue) to the south and shorter ice seasons throughout the PAL study area.
Using satellite and meteorological data of ice-climate variability (which extend our ship-based and near-shore based observations both seasonally and regionally), we investigate and evaluate how seasonality, a dominant phenological control of the marine ecosystem, is changing on space/time scales relevant to the ecology. Our large-scale analysis also indicates that the WAP region is particularly sensitive to El Niño Southern Oscillation (ENSO) and Southern Annular Mode (SAM) variability. For example, during the La Niña and +SAM that occurred in austral spring-autumn of 1998-99 (e.g., autumn in figure left, bottom panel), low atmospheric pressure anomalies west of the Antarctic Peninsula (blue contours) intensified warm northerly winds over the WAP, resulting in wind-driven sea ice decreases (earlier spring retreat and later autumn advance, the latter depicted here). The opposite occurs during El Niño and/or –SAM, e.g., the austral autumn in 1980 (figure right, top panel) when –SAM conditions produced high-pressure anomalies and cold southerly winds over the WAP and an earlier austral autumn sea ice advance. Within this context of climate sensitivity and change, and in conjunction with the other components, we strive to seasonally resolve how surface forcing, sea ice in particular, influences ocean mixed layer processes, and hence the biological and biogeochemical response of the marine ecosystem, through both observations and modeling studies.
Stammerjohn, S., T. Maksym, P. Heil, R. A. Massom, M. Vancoppenolle, and K. C. Leonard. 2011. The influence of winds, sea surface temperature and precipitation anomalies on Antarctic Regional sea ice conditions during IPY 2007, Deep Sea Research II 58, 999-1018, doi: 10.1016/j.dsr2.2010.10.026.
Stammerjohn, S. E., D. G. Martinson, R. C. Smith, X. Yuan and D. Rind. 2008. Trends in Antarctic annual sea ice retreat and advance and their relation to ENSO and Southern Annular Mode Variability. Journal of Geophysical Research 113, C03S90, doi: 10.1029/2007JC004269.
Stammerjohn, S. E., D. G. Martinson, R. C. Smith, and R. A. Iannuzzi. 2008. Sea ice in the western Antarctic Peninsula region: spatio-temporal variability from ecological and climate change perspectives. Deep Sea Research II, 55 doi: 10.1016/j.dsr2.2008.04.026.
Stammerjohn, S. E., M. R. Drinkwater, R. C. Smith, and X. Liu. 2003. Ice-atmosphere interactions during sea-ice advance and retreat in the western Antarctic Peninsula region, Journal of Geophysical Research, 108 (C10), 10.1029/2002JC001543.
Stammerjohn, S. E., and R. C. Smith. 1997. Opposing Southern Ocean climate patterns as revealed by trends in regional sea ice coverage. Climatic Change 37: 617-639.