气候变化领域集成服务门户(CCPortal): Distinguishing current effects in sediments delivered to the ocean by ice. I. Principles; methods and examples

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DOI	10.1016/j.quascirev.2019.03.031
	Distinguishing current effects in sediments delivered to the ocean by ice. I. Principles; methods and examples
	McCave I.N.; Andrews J.T.
发表日期	2019
ISSN	0277-3791
起始页码	92
结束页码	107
卷号	212
英文摘要	There are climatically important ocean flow systems in high latitudes, for example the East and West Greenland and Labrador Currents and Nordic Sea overflows in the North, and Antarctic Circumpolar Current in the South, for which it would be useful to know history of flow strength. Most of the sediment records under these flows contain evidence of supply from glacial sources, which has led to the supposition that fine sediment records, which in other settings provide evidence of vigour of flow from the sortable silt proxy, are fatally contaminated by unsorted glacial silt. It is suggested here that if the fine fraction (<63 μm) has been transported and sorted, then it does not matter that it may have been released from icebergs, sea ice or meltwater plumes. Here we show that correlation between sortable silt mean and percentage provides a good indicator of whether a fine sediment record has been sufficiently well current-sorted to provide a reliable flow history. The running downcore correlation (r run ) (5 to 9-point depending on sampling interval) is found to be optimal, and a value of r run < 0.5 is proposed as an indicator of sufficiently poor sorting to invalidate a section of mean size record. More than 40 grainsize records determined by laser particle sizers from over 30 core sites have been processed and examined for evidence of sorting. As expected, there is a tendency for poor sorting and unreliable records at points where the flow speed has decreased to very low values. There is no consistent relationship between the sorting of the fine fraction and the content of coarse ice-rafted debris (as long as the IRD fraction is not > 50%) because the two are not related. End member (EM) decomposition of several records yields variable results in terms of the relationship between EM ratios and grainsize parameters. Although such an approach can generate fine sediment parameters it does not provide a basis for deciding whether or not a record is acceptably current sorted and thus contains a valid flow speed proxy. Our proposed discrimination between current-sorted and unsorted fine fractions is applicable to all fine grained deposits, not only high-latitude deposits with coarse IRD. Examples from East Greenland, Faroe Bank Channel, Gardar Drift show mainly well sorted signatures. Amounts of coarse IRD range up to 60% with only those >50% having a consistent impact on sortable silt mean size. With the exception of a Southern Ocean site on the Antarctic continental rise where half the record is poorly sorted, the silt mean data are sufficiently well sorted to provide credible flow speed histories. This bodes well for the extraction of such histories from climatically important high-latitude flows such as the East Greenland Current. © 2019
英文关键词	Downcore correlation; East Greenland current; End member; Fine sediment; Ice-rafted debris; Ice-rafting; IRD; Labrador current; Laser sizers; Sortable silt
语种	英语
scopus关键词	Debris; Deposits; Glacial geology; Ocean currents; Screening; Sea ice; Silt; Sorting; East greenland currents; Endmembers; Fine sediments; Ice rafted debris; Ice rafting; Labrador Current; Laser sizer; Sediments; continental rise; correlation; current velocity; decomposition analysis; fine grained sediment; flow velocity; ice-rafted debris; oceanic current; sediment transport; silt; Antarctic Circumpolar Current; Arctic Ocean; Atlantic Ocean; East Greenland Current; Faroe Bank Channel; Gardar Drift; Southern Ocean; Southern Ocean; West Greenland Shelf
来源期刊	Quaternary Science Reviews
文献类型	期刊论文
条目标识符	http://gcip.llas.ac.cn/handle/2XKMVOVA/151947
作者单位	Godwin Laboratory for Palaeoclimate Research, Department of Earth Sciences, University of Cambridge, Downing Street, Cambridge, CB2 3EQ, United Kingdom; Department of Geological Sciences and INSTAAR, University of Colorado, Boulder, CO 80309, United States
推荐引用方式 GB/T 7714	McCave I.N.,Andrews J.T.. Distinguishing current effects in sediments delivered to the ocean by ice. I. Principles; methods and examples[J],2019,212.
APA	McCave I.N.,&Andrews J.T..(2019).Distinguishing current effects in sediments delivered to the ocean by ice. I. Principles; methods and examples.Quaternary Science Reviews,212.
MLA	McCave I.N.,et al."Distinguishing current effects in sediments delivered to the ocean by ice. I. Principles; methods and examples".Quaternary Science Reviews 212(2019).