Age constraints on subtropical iceberg scour events

GSTDTAP

项目编号	1558994
	Age constraints on subtropical iceberg scour events
	Jenna Hill
主持机构	Coastal Carolina University
项目开始年	2016
	2016-10-01
项目结束日期	2018-09-30
资助机构	US-NSF
项目类别	Standard Grant
项目经费	79404(USD)
国家	美国
语种	英语
英文摘要	As the ice sheets across North America melted following the last ice age, huge icebergs calved off into the sea, drifting in ocean currents across the North Atlantic. Many of these icebergs travelled east, remaining in polar regions, but new evidence from high-resolution maps of the seafloor, combined with modeling of past ocean currents, suggests hundreds of massive (~300m thick) icebergs likely drifted south along the Atlantic coast of the U.S., with some traveling all the way to the Florida Keys before completely melting. These icebergs would have been carried south by huge outburst floods of melting ice water that were able overcome the northward flow of the Gulf Stream current. The discovery of this pathway implies the circulation patterns of fresh meltwater from ice sheets and the subsequent impact on global climate may be more complex than previously thought; yet the timing of these events remains uncertain. The goal of this research is to provide initial age constraints on the timing of the iceberg scour events by examining seafloor sediment from this region and assess the potential to obtain high resolution records of cold, meltwater pulses flowing south along the margin. These data will present an important step forward in understanding how glacial meltwater pulses interact with and impact global circulation and climate patterns. Looking to ice sheet melting events in the past can provide critical insight to future changes, which is of particular interest as modern ice sheets in Greenland and Antarctica continue to melt and the impacts of shifts in global climate are felt around the world. Many abrupt shifts in Northern Hemisphere climate during the last 20,000 to 6,000 years are thought to have been triggered by the discharge of large volumes of meltwater and icebergs to the subpolar North Atlantic. The recent discovery of iceberg scours at subtropical latitudes (35-24°N), along with high-resolution numerical model reconstructions of associated meltwater floods, suggests that freshwater rapidly would have reached the subtropics without initially freshening the subpolar deepwater formation regions that moderate the strength of the Atlantic Meridional Overturning Circulation (AMOC). Freshwater associated with these events would have been significantly diluted by mixing with the saltier current before being advected northward to the subpolar gyre by the Gulf Stream. This pattern of subtropical freshening contrasts with the current paradigm that increased meltwater and iceberg discharge freshened the subpolar gyre, as shown by the presence of ice-rafted detritus (IRD) in marine sediments in the northern Atlantic. The analysis of marine sediment cores from the subtropical iceberg scours will help initiate the compilation of a paleoclimate database recording the frequency, duration and magnitude of meltwater and iceberg events routed to the subtropical North Atlantic. These data will provide critical model parameters describing the timing and conditions for grounded iceberg transport across the margin that can be used to examine whether the presence iceberg scours and IRD represent changes in large-scale ocean circulation, or more localized changes in the trajectory and location of melting icebergs. Understanding when meltwater and icebergs were transported to the subtropics is vital for unraveling how changes in high-latitude freshwater forcing may have influenced past climate.
URL	查看原文
文献类型	项目
条目标识符	http://119.78.100.173/C666/handle/2XK7JSWQ/70474
专题	环境与发展全球科技态势
推荐引用方式 GB/T 7714	Jenna Hill.Age constraints on subtropical iceberg scour events.2016.