Michael L. Prentice

Bio: Michael L. Prentice is an academic researcher from University of New Hampshire. The author has contributed to research in topics: Glacial period & Last Glacial Maximum. The author has an hindex of 10, co-authored 13 publications receiving 1550 citations. Previous affiliations of Michael L. Prentice include Indiana University & Durham University.

Major features and forcing of high-latitude northern hemisphere atmospheric circulation using a 110,000-year-long glaciochemical series

Abstract: The Greenland Ice Sheet Project 2 glaciochemical series (sodium, potassium, ammonium, calcium, magnesium, sulfate, nitrate, and chloride) provides a unique view of the chemistry of the atmosphere and the history of atmospheric circulation over both the high latitudes and mid-low latitudes of the northern hemisphere. Interpretation of this record reveals a diverse array of environmental signatures that include the documentation of anthropogenically derived pollutants, volcanic and biomass burning events, storminess over marine surfaces, continental aridity and biogenic source strength plus information related to the controls on both high- and low-frequency climate events of the last 110,000 years. Climate forcings investigated include changes in insolation of the order of the major orbital cycles that control the long-term behavior of atmospheric circulation patterns through changes in ice volume (sea level), events such as the Heinrich events (massive discharges of icebergs first identified in the marine record) that are found to operate on a 6100-year cycle due largely to the lagged response of ice sheets to changes in insolation and consequent glacier dynamics, and rapid climate change events (massive reorganizations of atmospheric circulation) that are demonstrated to operate on 1450-year cycles. Changes in insolation and associated positive feedbacks related to ice sheets may assist in explaining favorable time periods and controls on the amplitude of massive rapid climate change events. Explanation for the exact timing and global synchroneity of these events is, however, more complicated. Preliminary evidence points to possible solar variability-climate associations for these events and perhaps others that are embedded in our ice-core-derived atmospheric circulation records.

Stability of the Larsen B ice shelf on the Antarctic Peninsula during the Holocene epoch

Abstract: The stability of the Antarctic ice shelves in a warming climate has long been discussed, and the recent collapse of a significant part, over 12,500 km2 in area, of the Larsen ice shelf off the Antarctic Peninsula has led to a refocus toward the implications of ice shelf decay for the stability of Antarctica's grounded ice. Some smaller Antarctic ice shelves have undergone periodic growth and decay over the past 11,000 yr (refs 7-11), but these ice shelves are at the climatic limit of ice shelf viability and are therefore expected to respond rapidly to natural climate variability at century to millennial scales. Here we use records of diatoms, detrital material and geochemical parameters from six marine sediment cores in the vicinity of the Larsen ice shelf to demonstrate that the recent collapse of the Larsen B ice shelf is unprecedented during the Holocene. We infer from our oxygen isotope measurements in planktonic foraminifera that the Larsen B ice shelf has been thinning throughout the Holocene, and we suggest that the recent prolonged period of warming in the Antarctic Peninsula region, in combination with the long-term thinning, has led to collapse of the ice shelf.

Antarctic Glacial History Since the Last Glacial Maximum: An Overview of the Record on Land

Abstract: This overview examines available circum-Antarctic glacial history archives on land, related to developments after the Last Glacial Maximum (LGM). It considers the glacial-stratigraphic and morphologic records and also biostratigraphical information from moss banks, lake sediments and penguin rookeries, with some reference to relevant glacial marine records. It is concluded that Holocene environmental development in Antarctica differed from that in the Northern Hemisphere. The initial deglaciation of the shelf areas surrounding Antarctica took place before 10 000 14C yrs before present(BP), and was controlled by rising global sea level. This was followed by the deglaciation of some presently ice-free inner shelf and land areas between 10 000 and 8000 yr BP. Continued deglaciation occurred gradually between 8000 yr BP and 5000 yr BP. Mid-Holocene glacial readvances are recorded from various sites around Antarctica. There are strong indications of a circum-Antarctic climate warmer than today 4700–2000 yr BP. The best dated records from the Antarctic Peninsula and coastal Victoria Land suggest climatic optimums there from 4000–3000 yr BP and 3600–2600 yr BP, respectively. Thereafter Neoglacial readvances are recorded. Relatively limited glacial expansions in Antarctica during the past few hundred years correlate with the Little Ice Age in the Northern Hemisphere.

Stratigraphic profiling with ground-penetrating radar in permafrost: A review of possible analogs for Mars

Abstract: [1] We review our past and ongoing use of ground-penetrating radar to investigate permafrost in Alaska and in the Dry Valleys of Antarctica. The results may be relevant to radar efforts on Mars because of arid conditions and the presence of ice. The pulses were centered at 50, 100, and 400 MHz. We interpret profiles from two sites in the eastern Taylor Valley to show glaciolacustrine and glaciofluvial stratigraphy. The maximum depth of stratigraphy profiled there was about 33 m. Near Fairbanks, Alaska, the depth of penetration at 50 MHz was near 80 m in marginally frozen and stratified alluvial sands. At the Fairbanks sites, supplementary drilling was required to differentiate between reflections from conductive bedrock, a graphitic schist, and those from the water table at depths of 20–25 m. At a site on the North Slope of Alaska, we profiled present and remnant freezing fronts in an alluvial floodplain. The relative permittivity at most sites ranged between about 4 and 5.5, which is consistent with dry conditions, the mineralogy, and low ice content. Weak interface reflectivity or the lack of further interfaces may have limited the interpretation of maximum penetration where no water table was present because signal absorption should have been low and scarce diffractions imply that scattering was weak. The interface reflectivities beneath Taylor Valley may be a function of only density contrasts, since free water, and possibly ice, is absent.

On marine microfossil transport and pathways in Antarctica during the late Neogene: Evidence from the Sirius Group at Mount Fleming

Abstract: There are two extreme views of the evolution of the Pliocene Antarctic Ice Sheet. Dynamicists argue for ice-sheet reduction and reexpansion on the basis of Pliocene marine diatoms in a glacial deposit, the Sirius Group, that is widespread in the Transantarctic Mountains. Stabilists argue from other evidence that the Antarctic cryosphere remained essentially constant in area and volume; they propose marine diatom transport by eolian processes and emplacement into terrestrial glacial strata. Hence, the inferred source area and transport mechanism of marine diatoms are of critical importance. We tested the reduction hypothesis on an important outcrop of the Sirius Group at Mount Fleming, South Victoria Land. We observed very few, unidentifiable, marine diatom fragments in Sirius Group strata. In contrast, marine diatoms enclosed in a surface diamicton covering the Sirius Group were more abundant and identifiable. Our study further indicates that the Sirius Group at Mount Fleming was not deposited by the East Antarctic Ice Sheet but rather by alpine ice originating on the Transantarctic Mountains. On the basis of both data sets, we infer that marine diatoms postdate Sirius Group deposition at Mount Fleming and that transport was by wind, and we advance alternative scenarios for their source and transport pathways.

Persistent Solar Influence on North Atlantic Climate During the Holocene

Abstract: Surface winds and surface ocean hydrography in the subpolar North Atlantic appear to have been influenced by variations in solar output through the entire Holocene. The evidence comes from a close correlation between inferred changes in production rates of the cosmogenic nuclides carbon-14 and beryllium-10 and centennial to millennial time scale changes in proxies of drift ice measured in deep-sea sediment cores. A solar forcing mechanism therefore may underlie at least the Holocene segment of the North Atlantic's "1500-year" cycle. The surface hydrographic changes may have affected production of North Atlantic Deep Water, potentially providing an additional mechanism for amplifying the solar signals and transmitting them globally.

The Last Glacial Maximum.

Abstract: We used 5704 14C, 10Be, and 3He ages that span the interval from 10,000 to 50,000 years ago (10 to 50 ka) to constrain the timing of the Last Glacial Maximum (LGM) in terms of global ice-sheet and mountain-glacier extent. Growth of the ice sheets to their maximum positions occurred between 33.0 and 26.5 ka in response to climate forcing from decreases in northern summer insolation, tropical Pacific sea surface temperatures, and atmospheric CO2. Nearly all ice sheets were at their LGM positions from 26.5 ka to 19 to 20 ka, corresponding to minima in these forcings. The onset of Northern Hemisphere deglaciation 19 to 20 ka was induced by an increase in northern summer insolation, providing the source for an abrupt rise in sea level. The onset of deglaciation of the West Antarctic Ice Sheet occurred between 14 and 15 ka, consistent with evidence that this was the primary source for an abrupt rise in sea level ~14.5 ka.

Observed climate variability and change

Abstract: Chapter 2 emphasises change against a background of variability. The certainty of conclusions that can be drawn about climate from observations depends critically on the availability of accurate, complete and consistent series of observations. For many variables important in documenting, detecting, and attributing climate change, data are still not good enough for really firm conclusions to be reached. This especially applies to global trends in variables that have large regional variations, such as pre-