Seeking a Holocene drift ice proxy: non-clay mineral variations from the SW to N-central Iceland shelf: trends, regime shifts, and periodicities

Quantitative X-ray diffraction analysis of the <2 mm sediment fraction was carried out on 1257 samples (from the seafloor and 16 cores)from the Iceland shelf west of 18 degrees W. All but one core (B997-347PC) were from transects along troughs on the NW to N-central shelf, an area that in modern and historic times has been affected by drift ice. The paper focuses on the non-clay mineralogy of the sediments (excluding calcite and volcanic glass). Quartz and potassium feldspars occupy similar positions in an R-mode principal component analysis, and oligoclase feldspar tracks quartz; these minerals are used as a proxy for ice-rafted detritus (IRD). Accordingly, the sum of these largely foreign minerals (Q&K) (to Icelandic bedrock) is used as a proxy for drift ice. A stacked, equi-spaced 100 a record is developed which shows both low-frequency trends and higher-frequency events. The detrended stacked record compares well with the flux of quartz (mg cm(-2) a(-1)) at MD99-2269 off N Iceland. The multi-taper method indicated that there are three significant frequencies at the 95% confidence level with periods of ca. 2500, 445 and 304 a. Regime shift analysis pinpoints intervals when there was a statistically significant shift in the average Q&K weight %, and identifies four IRD-rich events separated by intervals with lower inputs. There is some association between peaks of IRD input, less dense surface waters (from delta O-18 data on planktonic foraminifera) and intervals of moraine building. Copyright (C) 2009 John Wiley & Sons, Ltd.