Milankovitch Forcing of Antarctic Climate in the Ross Sea Sector during the Quaternary
Kenneth L. Verosub, Luigi Jovane, Gary Acton and Fabio Florindo
Department of Geology, University of California, Davis, CA, 95616, USA.
Istituto Nazionale di Geofisica e Vulcanologia, Via di Vigna Murata 605, 00143, Roma, Italy.
Antarctica is a primary driver of global climate, but to date, there has been no clear evidence that the climate of the Ross Sea exhibits Milankovitich cyclicity. We have been studying the paleomagnetic and environmental magnetic properties of Eltanin 27-21, an 18-meter long piston core collected in the Ross Sea near Cape Adare in 1968 by the USNS Eltanin as part of Operation Deep Freeze. The magnetic polarity of 680 discrete samples from the core was used to develop an age model extending from the top of the Brunhes Chron to the Reunion Subchron. When converted to the time scale, the downcore variations of several environmental magnetic parameters exhibit features consistent with 40-ky cyclicity prior to the mid-Pleistocene transition and 100-ky cyclicity afterward. In order to better understand the nature of these features, we determined whether the environmental magnetic parameters had high or low values at each magnetic polarity boundary and compared that result with the marine oxygen isotope stage associated with the boundary. In general, high magnetic concentrations and finer magnetic grain-sizes occurred in interglacials while low concentrations and coarser grain-sizes occurred in glacials. These conclusions are consistent with findings from environmental magnetic studies of older (pre-Quaternary) sediments from other cores from the Ross Sea, such as CIROS-1 and the Cape Roberts Project. In those cores, increases in magnetic concentration and decreases in magnetic grain-size were associated with warmer, more humid conditions. Our results demonstrate for the first time that during the Quaternary, the climate of the Ross Sea sector was subject to Milankovitch forcing. They also provide a distal record of environmental magnetic paleoclimate proxies in the Ross Sea that can be compared with the proximal records being obtained from the ANDRILL project.
PP26: Polar Environmental Change, the Paleoceanographic Perspective: The International Polar Year
In order to place current dramatic changes in ice conditions and other oceanographic variables in the Polar areas in their proper perspective and to predict future scenarios, we need the geologic record of Polar change. The high latitudes play an important role in storing ice and in providing a non-linear response to orbital forcing via ice dynamics, a role that will certainly be important for future climate but has also been implicated in past records of climate change. Many questions remain, however, about the interpretation of proxy records of climatic variation: the spatial and temporal dynamics of climatic forcing and earth system response, and the synchroneity of northern and southern hemisphere response to forcing; these questions are often best addressed by paleoceanographic records.
Arctic paleoceanography has received a major boost from the 2004 ACEX expedition of deep-sea drilling on the Lomonosov Ridge and the 2005 Healy-Oden Trans-Arctic Expedition (HOTRAX). Prior to HOTRAX, the longest cores from the central Arctic (Mendeleev and Alpha Ridges) were about 7 meters. During the HOTRAX expedition, 29 piston cores averaging about 12 meters in core length plus accompanying multicores were collected from across the Arctic, producing a cache of over 450 meters of core with unprecedented potential to contribute to a paleoceanographic record that has lacked adequate core material to this date. In addition to the central Arctic cores, HOTRAX also collected eight piston cores and accompanying multicores from the shelf and continental slope off Barrow, Alaska with sedimentation rates of a half meter or more per thousand years. Initial results of the work begun on these HOTRAX and other core materials will be presented, leading to new insights into the mysteries of Arctic environmental change that is rapidly remaking the Arctic Ocean into an ice-free environment with profound implications for society.
Southern Ocean Paleoceanography has seen a similar renaissance, with several ODP and IODP expeditions over the past decade, a number of piston coring expeditions, and efforts at scientific ocean drilling along the margins of Antarctica. Furthermore, Southern Ocean Paleoceanography and cryospheric development is the focus of several IODP drilling proposals, to some extent the current and ongoing ANDRILL research efforts, and myriad continental ice-related studies to gauge the past and future stability of the large continental ice sheets to climate change.
This session will focus on sedimentary, paleobiological, and isotopic records of climatic variation and cryosphere development from both the northern and the southern hemisphere Polar oceans. The International Polar Year is highlighting the importance of high latitude environments, and this session explores how these environments have varied, especially from the Pliocene to present. We welcome contributions related to the evolution of sea-ice dynamics, biological productivity, hydrographic circulation and deep water formation, and high latitude maritime environments.
