Detecting the source of Heinrich layers: an organic geochemical study.
Abstract
There are controversies regarding the origin of Heinrich layer 3, the massive ice-rafting and meltwater event in the North Atlantic Ocean during the last glacial cycle spanning the time between 28 and 29 ka BP. Some argue in favor of a North American Laurentide Ice-Sheet (LIS) source similar to other Heinrich layers while a contending view argues for European ice-sheet sources. Existing geochemical proxies such as 40Ar/39Ar, 207Pb/206Pb, etc., could not be used to distinguish between different sources for H3 due to its low content of ice-rafted debris (IRD). In order to circumvent this problem we have used organo-geochemical tracers to characterize the sediment provenance of Heinrich layers 2 and 3 as well as samples between Heinrich layers. The samples analyzed are from cores covering a wide range of geographic locations from the mouth of the Hudson Strait at 62° N to 50° N in the Labrador Sea, the former main conduit of the LIS iceberg discharge, to as far south as the Bermuda Rise and to the east side of the Atlantic Ocean. Samples were analyzed for saturated and aromatic hydrocarbons by Gas Chromatography-Mass Spectrometry. Mature biomarkers such as hopanes and steranes in their thermodynamically stable configuration, and aromatic hydrocarbons such as aromatic steroids, aryl isoprenoids and aromatic hopanoids were detected. This assemblage of mature compounds is incompatible with recent and shallow surface sediment. Presence of such hydrocarbon compounds can be explained by the transportation of organic matter due to the glacial erosion of organic-rich source rocks. Our findings clearly demonstrate no appreciable differences in biomarkers distributions in sediments within H2 and H3 in the Labrador Sea. Biomarker patterns similar to those of the Labrador Sea sediments within H2 and H3 are present in the western Atlantic cores VM23-14 [43.24° N, 45.15° W] and-16 [46° N, 45° W]. The same signatures of biomarkers were also identified in core Hu89038-008 [33.69° N, 57.61° W] from the Bermuda Rise as well as in cores BOFS-5K [50.68° N, 21.86° E] and-8K [52.51° N, 22.07° E] from the eastern North Atlantic. Our data suggest that during the deposition of both H2 and H3 in the Labrador Sea as well as in the North Atlantic Ocean, sediments were delivered by icebergs that originated from the LIS. It also implies that the fine-grained sediments distinctive of the LIS source reached as far as 20oE in the North Atlantic, which is in agreement with the earlier findings of Rosell-Melé et al.(1997) in core BOFS-5K. Our results are in contrast to the existing paradigm that H3 only originated from a European source. The presence of similar mature biomarkers indicative of the LIS source in the Bermuda Rise core suggests that during the Heinrich and other stadial events LIS detritus were carried to the site by the Western Boundary Undercurrent (WBUC) and deep Gulf Stream circulation.
- Publication:
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AGU Spring Meeting Abstracts
- Pub Date:
- May 2004
- Bibcode:
- 2004AGUSMGC13A..04R
- Keywords:
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- 1055 Organic geochemistry;
- 3344 Paleoclimatology;
- 4267 Paleoceanography;
- 4558 Sediment transport