RECEIVED Thu, 15 Jul 1999 15:32:21 GMT Date: Thu, 15 Jul 1999 15:32:11 -0700 To: Joe Borkowski , Karl Newyear From: Raymond Smith Subject: NBP99-06 Weekly Report Cc: smithra@nbp.polar.org Content-Type: application/msword; name="july_10.doc" ***************************************************** NBP99-06 Weekly Report – 4 July – 11 July, 1999 (JD 185-192) The life histories of various polar marine species are synchronized with the seasonality of sea ice. Thus any temporal shifting of the annual cycle or regional sea ice coverage significantly changes the physical environment of any given season and, consequently, also affects those ecosystem variables that are timed to the mean annual cycle of sea ice. In the Palmer LTER (Western Antarctic Peninsula) area the mean annual cycle is characterized by a relatively short (about 5 months) period of ice advance, with peak ice extent occurring in August, followed by a longer period (about 7 months) of ice retreat. However, there is also significant interannual variability about the mean and this year is, at this time, below the mean for sea ice extent. In an average year, by mid-July sea ice extends over the southern third to one-half of the LTER grid. This year, as noted in an earlier weekly report, we encountered sea ice along the 300 line (about 66.5S). As we finish our cruise, the sea ice has retreated – rather than advanced - roughly 150km to the southwest (to about the 150 line, or 67.5S). If there is not a rapid advance in sea ice over the next six weeks, and if our hypotheses linking sea ice and various trophic levels hold true, this is likely to be a lean year for phytoplankton, krill and sea birds within the LTER area. Furthermore, these sea ice related processes will have a major influence on export production, local sequestration of atmospheric carbon dioxide and the intensity of pelagic/benthic coupling. A year round sediment trap mooring located within the LTER study area near Victor Hugo Island is in place to record these anomalous events if they occur. At the conclusion of our cruise we have now completed multi-day ice stations representing various stages of sea ice growth including: medium (70-120cm), thin (30-70cm) first-year ice, young ice (10-30cm), & new ice (<10cm) both nilas and frazil/new pancake. Sea ice has been characterized both physically and biologically for each of these sea ice stations. In addition, we have carried out CTD, water sample, net tows, optics, sea bird observatons & other LTER core measurements along the 200 and 600 cardinal lines. In addition, we succeeded in landing at Dion Island to carry out sea bird observations in the Special Permit Area (SPA). Our interdisciplinary efforts have focused on variations on seawater and sea ice habitats and on measurements of various processes associated with sea ice formation during this early winter period. These invaluable winter data will be compared to the mean & variance of our 6-year record of spring/summer conditions for this area to help understand controls on various processes within this seasonally phased ecosystem. The physical oceanography and modeling team (D. Martinson, LDGO & R. Iannuzzi) obtained 80 CTD profiles during the cruise that spanned the deeper sope waters to the shallow shelf areas. Mixed layer enthalpy content (relative to the freezing point) was computed for each station allowing us to estimate: heat loss necessary before ice formation, melt rate or ice growth rates. Other bulk characteristics of the upper water column were also estimated in order to determine the ocean-ice feedback potential. Here, as in the Weddell gyre region, the water bulk stability is imparted by the heat in the deeper water (Upper Circumpolar Deep Water), and for every unit of destabilization driven by ice growth, pycnocline characteristics suggest that two units of deep sensible heat would be released by entrainment. The microbiology and carbon flux team (D.Karl, Univ. Hawaii, K. Bjorkman, C. Carrillo, L. Fujieki, D. Hebel & A. Thomson-Bulldis) focused their efforts on documenting the standing stocks of Archaea and bacteria and on measurements of microheterotrophic processes. In particular, the wintertime dominance of Archaea, and the observed changes in the C:O elemental stoichiometry (C:N:P:Si) of exported particulate matter between summer and winter are key observations during this research effort. The phytoplankton team (M. Vernet, SIO, UCSD, M.E. Ferrario, M. Zirbel, I. Garibotti, B. Bradshaw & D. Hamm) carried our microscopic analysis and pigment composition of new ice and water column samples and found low cell abundance. Flagellates (mainly prymnesiophytes and crysophytes) numerically dominate phytoplankton communities. Diatoms dominate ice communities, even in 1-day ice, suggesting concentration of diatoms during ice formation. Phytoplankton are low-light adapted, with high chlorophyll_a fluorescence and high carotenoid to chl_a ratios, both in water column and ice communities. Overall primary production is low, in particular in areas South of the Antarctic Circle, but the efficiency of photosynthesis is similar to that found in summer. The krill team (L. Quitin, UCSB, J. Flaherty, J. Kneebone, S. Oakes, M. Scott, T. Shaw, J. White) towed a Mocness trawl in and out of pack ice to determine whether krill larvae occurred in both ice-covered and open-ocean areas, and weather they vertically migrate during late June to early July. Larvae were found in surface waters and did not vertically migrate. No krill larvae were found over shelf waters north of Adelaide Island. This lack of larvae and pack ice throughout the area sampled by the Pal LTER during the austral summer suggests that recruitment will be very low for krill this year. Diving observations of krill larvae under pack ice south of Marguerite Bay reconfirmed past observations that krill larvae are found in areas of over-rafted ice, primarily between floes this time of year, and are found feeding mostly on upward facing ice surfaces. Zooplankton tows will be compared with results from the austral summer and samples of krill larvae for condition factor, chemistry and growth rates analyzed at the Marine Science Institute at UCSB. Observations for sea birds and marine mammals have been been conducted throughout this cruise both underway and on station. Also, collections and stomach lavaging were carried out on the few occasions when possible. These results will be compared both with summer observations and previous winter cruise results. The sea ice/optics/remote sensing team (R. Smith, UCSB, J. Ukita, LDGO & NSDAJ, M. Colee, D. Menzies, T. Newberger, D. Sonier & S. Stammerjohn) have carried out snow/sea ice transects and zodiac sampling of various stages of sea ice. These various stages have also been characterized both physically, optically and biologically (chl_a concentrations). In addition, a frazil meter (Scott Pague, OSU) and an instrumented ROV have been used to measure frazil ice and to characterize the optical properties under sea ice. We began our last week by celebrating the 4th of July with a BBQ on the helo-deck (many thanks to Marta and her fine crew not only for the BBQ but also for the excellent food throughout the cruise) including a large cake decorated as a US flag. In true 4th of July tradition, we experienced a mid-winter heat wave south of the Antarctic Circle with the temperature hovering about 0C with light rain, not snow. We ended our week, having moved north into open water, by being hit by a deep low pressure system (958mb) with winds in excess of 50 knots. This ended our last day of sampling along the 600 line and prevented both another attempt at installing the AWS at Hugo Island and offloading equipment at Palmer Station. We have now ended science activities and are engrossed in packing, paper work and surviving the Drake crossing. Special thanks again go to Captain Joe Borkowski, Chief Mate Tom Baker, Mates Valdimir Repin & Paul Jarkiewicz and their fine crew for their always friendly, experienced and professional work. And to Karl Newyear and his ASA group for their outstanding support in all areas. Ray Smith, Chief Scientist NBP-06 Palmer LTER Sea Ice Cruise