El Nio-Southern Oscillation(ENSO)has affected penguins and their habitats in the western Antarctic Peninsula.We used both historical penguin population dynamics data(1980–2012)and sedimentary lipids in penguin droppings(1916–2001)on Ardley Island to examine the responses of the Antarctic ecosystem to ENSO(El Nin o/La Nin a)events.The results showed that during the last 30 years,climate,marine food chain changes,and human activity have significantly affected penguin population sizes on Ardley Island.The Chinstrap(Pygoscelis antarctica)and Ade′lie(P.adeliae)penguin populations showed a good correlation with ENSO events.The Chinstrap penguin population decreased significantly because it was more sensitive to increasing human disturbance(e.g.,scientific activity and tourism)than Ade′lie and Gentoo(P.papua),particularly during the breeding season.Compositional features of n-alkanes in penguin dropping sediments revealed that organic matter came from lower terrestrial plants,bacteria and algae.C23was the main nalkane heavy hydrocarbon indicating mosses and lichens in the penguin’s diet.Variation in the ratio of nC23/nC17was closely correlated with ENSO events.The bacteria intrusion index(ratio of(iC15:0?aC15:0)/nC15:0for fatty acids)reflected significant increases in microorganism activity during several periods in this area.Meanwhile,the CPIA value for fatty acids decreased because micro-organisms contributed light hydrocarbon fatty acids to penguin droppings.Our results showed that the fine structure and molecular indices of fatty acids and n-alkanes in penguin dropping sediments can be used to explain climate-driven microbial processes,and to reveal the important role that microbes and bacteria play in the relatively simple Antarctic ecosystem.
Haisheng ZhangJun ZhaoZhengbing HanBing LuHans-Ulrich Peter
The study provides one of the first lines of evidence showing linkages between Antarctic phytoplankton abundance and composition in response to ENSO, based on historical reconstruction of sediment biomarkers. In addition to sediment biomarkers, field measured and remote sensing data of phytoplankton abundance were also recorded from Prydz Bay, Eastern Antarctica. Com-munity structure of field measured phytoplankton showed significant El Ni？o/La Ni？a-related succession during 1990 to 2002. In general, the number of algae species decreased during El Ni？o and La Ni？a years compared to normal years. Austral summer monthly variation of remotely sensed chlorophyll-a （Chl-a）, particulate organic carbon （POC）, and sea surface temperature （SST） indicated that ENSO impacted the timing of phytoplankton blooms during 2007 to 2011. Phytoplankton blooms （indicated by Chl-a and POC） preceded the increases in SST during El Ni？o years, and lagged behind the SST increases during La Ni？a years. Stratigraphic record of marine sedimentary lipid （brassicasterol, dinosterol and alkenones） biomarkers inferred that the proportions of different algae （diatoms, dinoflagellates and haptophytes） changed significantly between El Ni？o and La Ni？a events. The relative proportion of diatoms increased, with that of dinoflagellates being decreased during El Ni？o years, while it was reversed during La Ni？a years.
The historical data of phytoplankton and chlorophyll a(Chl a)(1990–2002)obtained during the Chinese National Antarctic Research Expedition(CHINARE)in the Prydz Bay have been integrated.The results showed that the temperature,salinity,nutrients,and oxygen of seawater changed when El Nino/La Nina occurred.The variation of biological communities reflected the response of ecosystem to environmental changes.During El Ni?o period,Chl a concentration and phytoplankton community structure changed significantly,and the relative proportion of diatoms increased while dinoflagellates decreased.During La Ni?a period,the proportion of diatoms decreased,but the golden-brown algae and blue-green algae increased significantly.The variation of phytoplankton population directly affected the biodiversity of the bay,which were also quite sensitive to the marine environment changes.Meanwhile,the satellite remote sensing data of 2002–2011(December–March)have been used to study the temporal connection change of Chl a and phytoplankton in the Prydz Bay.We found that there were significant differences in the monthly variation characteristics of satellite remote sensing Chl a and sea surface temperature(SST),which had some links with sea ice melting and El Ni?o/La Ni?a events.We found that the start time of bloom advanced,lagged or synchronized with the changes of the SST,and we also found the occurrence time of phytoplankton bloom corresponded with the sea ice melting inner bay.To some extent,this study will help us understand the relationships between ENSO events and the phytoplankton bloom in the Southern Ocean.
