Biogenic particles in antarctic ice cores and the source of antarctic dust
Biogenic particles in antarctic ice cores and the source of antarctic dust
To address questions on the origin of dust in antarctic ice cores, we sampled levels representing the Holocene and last glacial maximum in Dome C and Vostok cores from the central Antarctic Plateau (Lorius et al. 1979; Thompson, MosleyThompson, and Petit 1979; Petit, Briat, and Royer 1981). Preparation methods are described in Gayle y and Ram (1984). Our intention was to examine and identify biogenic particles (mainly diatoms) in the dust and determine, if possible, their source. Dome C and Vostok were selected because: • We observed diatoms in our preliminary analysis of Dome C. • There are no locally derived diatoms because both sites are too cold for summer meltpools to develop. • Given these considerations, any diatoms or other biogenic particles found in Dome C or Vostok ice are presumed to be eolian in origin. Diatoms, although rare in Vostok and Dome C ice, were present in both the Holocene and last glacial maximum, but concentrations were greater during the last glacial maximum (by about a factor of 20; Ram, Gayley, and Petit in press). In addition to broken specimens, which frequently could be identified only with difficulty to the genus or species level, we also found intact specimens which showed little or no signs of wear. In some cases, whole frustules were recovered. Species
There are extensive possible sources for marine diatoms on and around Antarctica, and the presence of almost exclusively fresh-water diatoms in Dome C and Vostok ice was not expected. [Similarly, the presence of mostly fresh-water diatoms in Greenland ice (Gayley and Ram 1984) was not expected, given the proximity to marine sources and the fact that an ice sheet covers more than 90 percent of the land surface.] There are three possible local sources for marine diatoms on and around Antarctica. These include wind and biotic transport from the southern ocean, which is largely ice free from 1 to 6 months during the summer and was the most probable source for increased marine aerosols in antarctic ice during the last glacial maximum (De Angelis et al. 1987). There are also deposits of marine diatoms in coastal regions of the antarctic continent. In addition to the fossil deposit (Pliocene) described by Pickard et al. (1987), there are extensive deposits (some of them more than 0.5 meter thick) of diatom-bearing penguin droppings in rookeries along the coast. We examined some of these droppings and found them to contain from 5 to 10 percent diatoms, all of marine origin. Given the above considerations, the southern ocean and, possibly, penguin rookeries would appear to be a more logical source for any diatoms found in antarctic ice. The fact that marine diatoms are rare in the ice argues against a local source for this component and, when combined with the observation that pollen grains also occur in the ice, suggests a largely extraantarctic source for dust found in ice cores. Empty diatom valves and frustules of both marine and fresh-water origin are known to be transported considerable distances. We believe that the fresh-water diatoms in Dome C and Vostok ice cores came from fossil sources with a very small component coming from the coeval southern ocean. Since the pollen grains suggest a semi-arid source and since the associated diatom assemblage rules out a sub-Saharan source, we speculate that the dust originated from the southern part of South America. We postulate this region as a source rather than Australia or New Zealand for the following reasons: • It extends further to the south than these two regions. • During the last glacial maximum the Polar Front extended further to the north in the Atlantic sector than any other sector of the southern ocean (Hays et al. 1976). • Storms generated at the Polar Front tend to spiral southward toward the continent. • Given these considerations, dust picked up in South America could easily be entrained in storms along the Polar Front and transported to Antarctica. This research was supported, in part, by National Science Foundation grant DPP 84-00575 to L.H. Burckle and by DPP 86-19198 to M. Ram and R.I. Gayley.
present included Navicula muticopsis, N. shackletonii, N. mutica var. cohnii, N. deltaica, and Cyclotella stellaris, as well as Pinnularia sp. and Cocconeis sp. All of these forms are known from
References
L.H. BURCKLE Lamont-Doherty Geological Observa tort,' Palisades, New York 10964
R.I. GAYLEY and M. RAM Department of Plnsics and Astronoint,' State University of New York Buffalo, New York 14260
J-R. PETIT Laboratoire de Glaciologie et Geophysique de l'Environinent 38031 Grenoble Cedex, France
fresh water lakes and fossil deposits on Antarctica (Kellogg and Kellogg 1987), but some are also known from high northern latitude localities. We also observed a fragment of what appeared to be the marine diatom Nitzschia kerquelensis. This species presently thrives in southern-ocean waters between approximately the Subantarctic Front and the Antarctic Slope Front (Burckle, Jacobs, and McLaughlin 1987). However, 98 percent of the diatoms in Dome C and Vostok samples were fresh water in origin. In addition to diatoms, we also found pollen grains (though their occurrence was rare), including a chenopod and a grass pollen (Graminae) which could not have had an antarctic source. 1988 REVIEW
Burckle, L.H., S.S. Jacobs, and R.B. McLaughlin. 1987. Late spring diatom distribution between New Zealand and the Ross Sea: Correlation with hydrography and bottom sediments. Micropaleontology, 33, 74-81. De Angelis, M., N.I. Barkov, and V.N. Petrov. 1987. Aerosol concentrations over the last climate cycle (160 kyr) from an Antarctic ice core. Nature, 325, 318-321. Gayley, RI., and M. Ram. 1984. Observation of diatoms in Greenland ice. Arctic, 37, 172-174. Hays, J.D., N.J. Shackleton, and G. Irving. 1976. Reconstruction of the Atlantic and western Indian ocean sectors of the 18,000 B.P. Antarctic ocean. Geological Society of America, Memoir 145, 337-372.
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Kellogg, D., and T. Kellogg. 1987. Diatoms of the McMurdo Ice Shelf, Antarctica: Implications for sediment and biotic reworking. Palaeogeography, Palaeoclimatology, Palaeoecology, 60, 77-96. Lorius, C., L. Merlivat, J. Jouzel, and M. Pourchet. 1979. A 30,000 year isotope climatic record from Antarctic ice. Nature, 280, 644-648. Petit, J-R., M. Briat, and A. Royer. 1981. Ice age aerosol content from east Antarctic ice core samples and past wind strength. Nature, 293, 391-394. Pickard, J., D.A. Adamson, D.M. Harwood, C.H. Miller, P.C. Quilty, and R.K. Dell. 1986. Early Pliocene sediments in the Vestfold Hills,
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east Antarctica; implications for coastline, ice sheet and climate. South African Journal of Science, 82, 520-521. Ram, M., R.I. Gayley, and J-R. Petit. In press. Insoluble particles in Antarctic ice: Background aerosol size distribution and diatom concentration. Journal of Geophysical Research. Thompson, L.C., E. Mosley-Thompson, and J-R. Petit. 1979. Glaciological interpretation of microparticle concentrations from the French 905-rn Dome C, Antarctica core, in Sea level, ice and climatic change. Proceedings of the Canberra Symposium. International Association of Hydrological Sciences, publication number 131, 227-234.
ANTARCTIC JOURNAL
To address questions on the origin of dust in antarctic ice cores, we sampled levels representing the Holocene and last glacial maximum in Dome C and Vostok cores from the central Antarctic Plateau (Lorius et al. 1979; Thompson, MosleyThompson, and Petit 1979; Petit, Briat, and Royer 1981). Preparation methods are described in Gayle y and Ram (1984). Our intention was to examine and identify biogenic particles (mainly diatoms) in the dust and determine, if possible, their source. Dome C and Vostok were selected because: • We observed diatoms in our preliminary analysis of Dome C. • There are no locally derived diatoms because both sites are too cold for summer meltpools to develop. • Given these considerations, any diatoms or other biogenic particles found in Dome C or Vostok ice are presumed to be eolian in origin. Diatoms, although rare in Vostok and Dome C ice, were present in both the Holocene and last glacial maximum, but concentrations were greater during the last glacial maximum (by about a factor of 20; Ram, Gayley, and Petit in press). In addition to broken specimens, which frequently could be identified only with difficulty to the genus or species level, we also found intact specimens which showed little or no signs of wear. In some cases, whole frustules were recovered. Species
There are extensive possible sources for marine diatoms on and around Antarctica, and the presence of almost exclusively fresh-water diatoms in Dome C and Vostok ice was not expected. [Similarly, the presence of mostly fresh-water diatoms in Greenland ice (Gayley and Ram 1984) was not expected, given the proximity to marine sources and the fact that an ice sheet covers more than 90 percent of the land surface.] There are three possible local sources for marine diatoms on and around Antarctica. These include wind and biotic transport from the southern ocean, which is largely ice free from 1 to 6 months during the summer and was the most probable source for increased marine aerosols in antarctic ice during the last glacial maximum (De Angelis et al. 1987). There are also deposits of marine diatoms in coastal regions of the antarctic continent. In addition to the fossil deposit (Pliocene) described by Pickard et al. (1987), there are extensive deposits (some of them more than 0.5 meter thick) of diatom-bearing penguin droppings in rookeries along the coast. We examined some of these droppings and found them to contain from 5 to 10 percent diatoms, all of marine origin. Given the above considerations, the southern ocean and, possibly, penguin rookeries would appear to be a more logical source for any diatoms found in antarctic ice. The fact that marine diatoms are rare in the ice argues against a local source for this component and, when combined with the observation that pollen grains also occur in the ice, suggests a largely extraantarctic source for dust found in ice cores. Empty diatom valves and frustules of both marine and fresh-water origin are known to be transported considerable distances. We believe that the fresh-water diatoms in Dome C and Vostok ice cores came from fossil sources with a very small component coming from the coeval southern ocean. Since the pollen grains suggest a semi-arid source and since the associated diatom assemblage rules out a sub-Saharan source, we speculate that the dust originated from the southern part of South America. We postulate this region as a source rather than Australia or New Zealand for the following reasons: • It extends further to the south than these two regions. • During the last glacial maximum the Polar Front extended further to the north in the Atlantic sector than any other sector of the southern ocean (Hays et al. 1976). • Storms generated at the Polar Front tend to spiral southward toward the continent. • Given these considerations, dust picked up in South America could easily be entrained in storms along the Polar Front and transported to Antarctica. This research was supported, in part, by National Science Foundation grant DPP 84-00575 to L.H. Burckle and by DPP 86-19198 to M. Ram and R.I. Gayley.
present included Navicula muticopsis, N. shackletonii, N. mutica var. cohnii, N. deltaica, and Cyclotella stellaris, as well as Pinnularia sp. and Cocconeis sp. All of these forms are known from
References
L.H. BURCKLE Lamont-Doherty Geological Observa tort,' Palisades, New York 10964
R.I. GAYLEY and M. RAM Department of Plnsics and Astronoint,' State University of New York Buffalo, New York 14260
J-R. PETIT Laboratoire de Glaciologie et Geophysique de l'Environinent 38031 Grenoble Cedex, France
fresh water lakes and fossil deposits on Antarctica (Kellogg and Kellogg 1987), but some are also known from high northern latitude localities. We also observed a fragment of what appeared to be the marine diatom Nitzschia kerquelensis. This species presently thrives in southern-ocean waters between approximately the Subantarctic Front and the Antarctic Slope Front (Burckle, Jacobs, and McLaughlin 1987). However, 98 percent of the diatoms in Dome C and Vostok samples were fresh water in origin. In addition to diatoms, we also found pollen grains (though their occurrence was rare), including a chenopod and a grass pollen (Graminae) which could not have had an antarctic source. 1988 REVIEW
Burckle, L.H., S.S. Jacobs, and R.B. McLaughlin. 1987. Late spring diatom distribution between New Zealand and the Ross Sea: Correlation with hydrography and bottom sediments. Micropaleontology, 33, 74-81. De Angelis, M., N.I. Barkov, and V.N. Petrov. 1987. Aerosol concentrations over the last climate cycle (160 kyr) from an Antarctic ice core. Nature, 325, 318-321. Gayley, RI., and M. Ram. 1984. Observation of diatoms in Greenland ice. Arctic, 37, 172-174. Hays, J.D., N.J. Shackleton, and G. Irving. 1976. Reconstruction of the Atlantic and western Indian ocean sectors of the 18,000 B.P. Antarctic ocean. Geological Society of America, Memoir 145, 337-372.
71
Kellogg, D., and T. Kellogg. 1987. Diatoms of the McMurdo Ice Shelf, Antarctica: Implications for sediment and biotic reworking. Palaeogeography, Palaeoclimatology, Palaeoecology, 60, 77-96. Lorius, C., L. Merlivat, J. Jouzel, and M. Pourchet. 1979. A 30,000 year isotope climatic record from Antarctic ice. Nature, 280, 644-648. Petit, J-R., M. Briat, and A. Royer. 1981. Ice age aerosol content from east Antarctic ice core samples and past wind strength. Nature, 293, 391-394. Pickard, J., D.A. Adamson, D.M. Harwood, C.H. Miller, P.C. Quilty, and R.K. Dell. 1986. Early Pliocene sediments in the Vestfold Hills,
72
east Antarctica; implications for coastline, ice sheet and climate. South African Journal of Science, 82, 520-521. Ram, M., R.I. Gayley, and J-R. Petit. In press. Insoluble particles in Antarctic ice: Background aerosol size distribution and diatom concentration. Journal of Geophysical Research. Thompson, L.C., E. Mosley-Thompson, and J-R. Petit. 1979. Glaciological interpretation of microparticle concentrations from the French 905-rn Dome C, Antarctica core, in Sea level, ice and climatic change. Proceedings of the Canberra Symposium. International Association of Hydrological Sciences, publication number 131, 227-234.
ANTARCTIC JOURNAL
