Response of Iberian Margin sediments to orbital and suborbital forcing over the past 420 ka

Abstract

[1] Here we report 420 kyr long records of sediment geochemical and color variations from the southwestern Iberian Margin. We synchronized the Iberian Margin sediment record to Antarctic ice cores and speleothem records on millennial time scales and investigated the phase responses relative to orbital forcing of multiple proxy records available from these cores. Iberian Margin sediments contain strong precession power. Sediment "redness" (a* and 570-560 nm) and the ratio of long-chain alcohols to n-alkanes (C 26 OH/(C 26 OH + C 29 )) are highly coherent and in-phase with precession. Redder layers and more oxidizing conditions (low alcohol ratio) occur near precession minima (summer insolation maxima). We suggest these proxies respond rapidly to low-latitude insolation forcing by wind-driven processes (e.g., dust transport, upwelling, precipitation). Most Iberian Margin sediment parameters lag obliquity maxima by 7-8 ka, indicating a consistent linear response to insolation forcing at obliquity frequencies driven mainly by high-latitude processes. Although the lengths of the time series are short (420 ka) for detecting 100 kyr eccentricity cycles, the phase relationships support those obtained by Shackleton [2000]. Antarctic temperature and the Iberian Margin alcohol ratios (C 26 OH/ (C 26 OH + C 29 )) lead eccentricity maxima by 6 kyr, with lower ratios (increased oxygenation) occurring at eccentricity maxima. CO 2 , CH 4 , and Iberian SST are nearly in phase with eccentricity, and minimum ice volume (as inferred from Pacific d 18 O seawater ) lags eccentricity maxima by 10 kyr. The phase relationships derived in this study continue to support a potential role of the Earth's carbon cycle in contributing to the 100 kyr cycle.

Aligning and synchronization of MIS5 proxy records from Lake Ohrid (FYROM) with independently dated Mediterranean archives: implications for DEEP core chronology

“…stable isotopes, Regattieri et al, 2014). Considering that marine chronologies, beyond the limit of radiocarbon dating methods, are often based on astronomical assumptions, it is now also common to transfer independently dated speleothems chronologies to marine records (Bar-Matthews et al, 2000;Almogi-Labin et al, 2009;Drysdale et al, 2007Drysdale et al, , 2009Grant et al, 2012;Ziegler et al, 2010;Hodell et al, 2013;Marino et al, 2015;Jiménez-Amat and Zahn, 2015). This can be somewhat problematic, as the assumption of synchronicity between speleothem and marine proxy records is not necessarily straightforward (e.g.…”

The "Shackleton Site" (IODP Site U1385) on the Iberian Margin

“…The similarity of some of the millennialscale events offer the opportunity of synchronizing the records and transferring the U-Th-dated chronology of the speleothem record to the ice core and marine sediment archives. Figure reproduced with permission from the American Geophysical Union (Hodell et al, 2013).…”

“…The site is located on a spur, the Promonotorio dos Principes de Avis, along the continental slope of the southwestern Iberian margin, which is elevated above the abyssal plain and influence of turbidites. The site is near the position of piston core MD01-2444, which has provided a remarkable record of millennial-scale climate variability of the last 190 ka (Vautravers and Shackleton, 2006; Skinner et al, 2007;Margari et al, 2010;Martrat et al, 2007;Hodell et al, 2013). The water depth (2578 m b.s.l.)…”

“…Similarly, Chinese speleothem records also contain millennial-scale "weak monsoon events" that have been correlated to cold phases in the North Atlantic (Cheng et al, 2009). A potential approach for further refining the absolute timescale of Site U1385 will be to correlate the prominent minima in Ca/Ti (corresponding to severe cold events) to weak monsoon events in the speleothem records (Hodell et al, 2013). For the last 800 ka, a "synthetic Greenland" record has been produced by extracting and differentiating the high-frequency variability from the Antarctic EPICA-Dome C ice core record (Barker et al, 2011).…”

“…, and E (black) from Site U1385. The spliced Ca/Ti record (red) is comprised of segments from Holes A, B, D, and E. Ca/Ti is a proxy for weight %CaCO 3 content and reflects the relative proportion of biogenic carbonate and detrital sediment (Hodell et al, 2013).…”