NOAA/WDS Paleoclimatology - Iceland Shelf 12KYr Quartz and K-Feldspar IRD Data

Quantitative X-ray diffraction analysis of the < 2mm sediment fraction was carried out on 1257 samples (from the seafloor and 16 cores) from the Iceland shelf west of 18°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-yr 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/cm2/yr) at MD99-2269 off N Iceland. The multi taper method (MTM) indicated that there are three significant frequencies at the 95% confidence level with periods of ~2500, 445, and 304 yr. Regime shift analysis pinpoints intervals when there was a statistically significant shifts 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 18O data on planktonic foraminifera), and intervals of moraine building.