Research Interests
- Millennial-scale North Atlantic paleoclimate and paleoceanographic variability during the last 0.5 Myr. One of the most remarkable and precise evidence of abrupt climate change during the last glacial period have been documented in ice-cores as well as in marine and terrestrial records. These are known as the Dansgaard-Oeschger cycles which are bundled into Bond cycles of 5-10 ka and terminated by Heinrich Events, the massive iceberg rafting events from the North American ice-sheet, which released enormous amounts of meltwater. As a result, the freshwater is assumed to disrupt or even halt the formation of NADW preventing the penetration of the North Atlantic Current into higher northern latitudes. We documented these Heinrich and other high-frequency events in detail from the Labrador Sea and northwest Atlantic Ocean for the last glacial cycle. Sediments samples from the Integrated Ocean Drilling Program (IODP) Expedition 306 allowed us to extend our records of these ice-rafting events to the last four glacial cycles. Mg/Ca-SST and Cd/Ca techniques are used to reconstruct the surface and deep water perturbation as a result of the ice-rafting which are sourced from the neighboring continental ice-sheets.
- Indian Ocean Monsoon (IOM) variability: The IOM is one of the major components of the modern tropical climate systems which is making profound changes in the lives of billions. Research over the last five years from in and around the tropics has shown a considerable degree of variability between the early and late Holocene which is attributed to the migration of the Intertropical convergence zone (ITCZ). With the potential warming looming in the horizon, it is predicted that the global climate might turn into like the early Holocene. But then the question is: what were the characteristics of IOM system during the early Holocene? What was the magnitude of runoff from the major rivers draining the Indian subcontinent as a result of the change in the intensity of monsoon? We have been working on the IOM project since 2005 and have reconstructed the first paleoclimatic history over the last 25 ka BP by making paired Mg/Ca and δ18O measurements on foraminiferal calcite in sediment cores retrieved from the Andaman Sea. We are working to extend this record to the Bay of Bengal and last three glacial cycles.
- Paleoceanography of the Labrador Sea and northwest Atlantic Ocean.
Studies over the last decade dedicated to assess the
impact of freshwater and sediment release through the Hudson Strait and St. Lawrence Channel to modulate the Atlantic meridional
overturning circulation (AMOC). Wallace Broecker of the LDEO of Columbia University suggested that the "outflow" from the St.
Lawrence River was the main impetus causing the Younger Dryas cooling in the Northern Hemisphere by perturbing the NADW formation.
However, later studies such as Anne de Vernal of UQAM questioned such a possibility. Keigwin and Boyle (1999) showed that the
ice-rafted debris (IRD) were present in a core from the Bermuda Rise. Given the geographic location of the Bermuda Rise and the
extent of the subtropical gyre in the northwest Atlantic, it was difficult to explain the occurrence of IRD at the Bermuda Rise.
We have been using sediment cores collected off seaward of Hudson Strait and St. Lawrence Channel to explore whether YD and other freshwater signals can be documented. We also collected acquired deep-tow seismic profiles and sediment cores from the northern Sohm Abyssal Plain of the northwest North Atlantic. Our preliminary data suggest that the Hudson Strait was an important source for freshwater and sediment during the YD and other younger freshwater forcing events. - Artic Rivers Outflow history during warmer times. Studies over the last decade suggest that the summer Arctic sea-ice may disappear by 2020, a faster rate than most modelers anticipated. Such a forecast is important to the freshwater budget around the circum-Arctic as well as to the freshwater fluxes through the Bering and Fram Straits. To assess the Arctic Ocean freshwater delivery to the site of Meridional Overturning Circulation, the need to study past changes in such fluxes and summer sea-ice is required. In this regard, the last interglacial interval may be used as an analog for projected future conditions. Two novel proxies, Mg/Ca and Ba/Ca in planktonic foraminifera, are promising as revealed from the reconstruction of tropical rivers freshwater outflow which have not been employed in the Arctic Ocean. Estimating absolute temperatures based on Mg/Ca values alone may not be possible in the Arctic Ocean because the sensitivity of Mg/Ca at low temperature in Neogloboquadrina pachyderma (sinistral). Nevertheless, variations in Mg/Ca compared to δ18O will characterize relative temperature changes. The Ba/Ca in planktonic foraminifera has recently been shown as a proxy for freshwater input. We have started working on this project from 2008! We utilizing sediment cores collected during the HOTRAX 2005 expedition.
My research interests involve resolving millennial-scale climate and ocean circulation variability from polar to tropical climate setting. I am also interested in understanding the dynamics of the Late Pleistocene Laurentide Ice-sheet and concomitant sediment and freshwater discharge-climate link which modulates the formation of the North Atlantic Deep water (NADW) and Labrador Sea Water (LSW). My current research projects can be grouped into the following: