Alfred Wegener Institute for Polar and Marine Research

About: Alfred Wegener Institute for Polar and Marine Research is a facility organization based out in Bremerhaven, Germany. It is known for research contribution in the topics: Sea ice & Arctic. The organization has 3359 authors who have published 10759 publications receiving 499623 citations. The organization is also known as: AWI & Alfred Wegener Institut.

Links between iron supply, marine productivity, sea surface temperature, and CO2 over the last 1.1 Ma

Abstract: Received 3 July 2008; revised 9 October 2008; accepted 27 October 2008; published 14 February 2009 [1] Paleoclimatic reconstructions have provided a unique data set to test the sensitivity of climate system to changes in atmospheric CO2 concentrations However, the mechanisms behind glacial/interglacial (G/IG) variations in atmospheric CO2 concentrations observed in the Antarctic ice cores are still not fully understood Here we present a new multiproxy data set of sea surface temperatures (SST), dust and iron supply, and marine export productivity, from the marine sediment core PS2489-2/ODP Site 1090 located in the subantarctic Atlantic, that allow us to evaluate various hypotheses on the role of the Southern Ocean (SO) in modulating atmospheric CO2 concentrations back to 11 Ma We show that Antarctic atmospheric temperatures are closely linked to changes in SO surface temperatures over the last 800 ka and use this to synchronize the timescales of our marine and the European Project for Ice Coring in Antarctica (EPICA) Dome C (EDC) records The close correlation observed between iron inputs and marine export production over the entire interval implies that the process of iron fertilization of marine biota has been a recurrent process operating in the subantarctic region over the G/IG cycles of the last 11 Ma However, our data suggest that marine productivity can only explain a fraction of atmospheric CO2 changes (up to around 40‐50 ppmv), occurring at glacial maxima in each glacial stage In this sense, the good correlation of our SST record to the EDC temperature reconstruction suggests that the initial glacial CO2 decrease, as well as the change in the amplitude of the CO2 cycles observed around 400 ka, was most likely driven by physical processes, possibly related to changes in Antarctic sea ice extent, surface water stratification, and westerly winds position

Orbitally driven east-west antiphasing of South American precipitation

Abstract: The variations of tropical precipitation are antiphased between the hemispheres on orbital timescales. A comparison between a speleothem record of precipitation in northeast Brazil and rainfall reconstructions from the rest of tropical South America shows that a similar antiphasing operated in the same hemisphere during the Holocene. The variations of tropical precipitation are antiphased between the hemispheres on orbital timescales. This antiphasing arises through the alternating strength of incoming solar radiation in the two hemispheres, which affects monsoon intensity and hence the position of the meridional atmospheric circulation of the Hadley cells1,2,3,4. Here we compare an oxygen isotopic record recovered from a speleothem from northeast Brazil for the past 26,000 years with existing reconstructions of precipitation in tropical South America5,6,7,8. During the Holocene, we identify a similar, but zonally oriented, antiphasing of precipitation within the same hemisphere: northeast Brazil experiences humid conditions during low summer insolation and aridity when summer insolation is high, whereas the rest of southern tropical South America shows opposite characteristics. Simulations with a general circulation model that incorporates isotopic variations support this pattern as well as the link to insolation-driven monsoon activity. Our results suggest that convective heating over tropical South America and associated adjustments in large-scale subsidence over northeast Brazil lead to a remote forcing of the South American monsoon, which determines most of the precipitation changes in the region on orbital timescales.

Changes in Arctic sea ice result in increasing light transmittance and absorption

Abstract: [1] Arctic sea ice has declined and become thinner and younger (more seasonal) during the last decade. One consequence of this is that the surface energy budget of the Arctic Ocean is changing. While the role of surface albedo has been studied intensively, it is still widely unknown how much light penetrates through sea ice into the upper ocean, affecting sea-ice mass balance, ecosystems, and geochemical processes. Here we present the first large-scale under-ice light measurements, operating spectral radiometers on a remotely operated vehicle (ROV) under Arctic sea ice in summer. This data set is used to produce an Arctic-wide map of light distribution under summer sea ice. Our results show that transmittance through first-year ice (FYI, 0.11) was almost three times larger than through multi-year ice (MYI, 0.04), and that this is mostly caused by the larger melt-pond coverage of FYI (42 vs. 23%). Also energy absorption was 50% larger in FYI than in MYI. Thus, a continuation of the observed sea-ice changes will increase the amount of light penetrating into the Arctic Ocean, enhancing sea-ice melt and affecting sea-ice and upper-ocean ecosystems.

Testing the direct effect of CO2 concentration on a bloom of the coccolithophorid Emiliania huxleyi in mesocosm experiments

Abstract: We studied the direct effects of CO2 and related changes in seawater carbonate chemistry on marine planktonic organisms in a mesocosm experiment. In nine outdoor enclosures (~11 m3 each), the partial pressure of CO2 (pCO2) in the seawater was modified by an aeration system. The triplicate mesocosm treatments represented low (~190 parts per million by volume (ppmV) CO2), present (~410 ppmV CO2), and high (~710 ppmV CO2) pCO2 conditions. After initial fertilization with nitrate and phosphate a bloom dominated by the coccolithophorid Emiliania huxleyi occurred simultaneously in all of the nine mesocosms; it was monitored over a 19-day period. The three CO2 treatments assimilated nitrate and phosphate similarly. The concentration of particulate constituents was highly variable among the replicate mesocosms, disguising direct CO2-related effects. Normalization of production rates within each treatment, however, indicated that the net specific growth rate of E. huxleyi, the rate of calcification per cell, and the elemental stoichiometry of uptake and production processes were sensitive to changes in pCO2. This broad influence of CO2 on the E. huxleyi bloom suggests that changes in CO2 concentration directly affect cell physiology with likely effects on the marine biogeochemistry.