Abstract
Laminated sediments of the continental slope off the Makran coast in the northern Arabian Sea are well-known climate archives and record productivity, as well as supply of material from land. Here, we studied sediment core 275KL off Pakistan in concert with sediment trap, dust and river samples in order to characterize and quantify land-derived material deposited in varves and event layers. We analysed grain sizes, mineral assemblages, bulk components and stable isotopes (δ13C, δ18O) of carbonates. In winter, enhanced river discharge is the main source of lithogenic matter contributing the major amounts to the total annual sedimentation of the northern Arabian Sea. During the late summer season, lithogenic matter accumulation is slightly enhanced, probably carried along with the south-eastward blowing Levar winds from the Balochistan and the Sistan Basins and the summer monsoon discharge maximum of perennial streams. C/N ratios and stable carbon and oxygen isotopes could not be used to distinguish between organic matter produced on land and in the ocean, whereas stable carbon and oxygen isotope ratios of carbonates suggest that sedimentation of event layers is dominated by direct inputs from land. Catastrophic denudation and storm events occur on average once every 50 years and lead to sedimentation rates that exceed the mean annual sedimentations of 983 g m−2 yr−1 by 6 to 10 times. Nevertheless, due to their rare occurrence, they contributed only 7% to the total sedimentation during the last ca. 5000 years. End-member modelling of grain sizes in accordance with lithogenic matter accumulation rates and event layer frequencies showed that arid conditions prevailed between 4000 and 5000 a BP while more humid conditions commenced around 2000 ka BP in accordance with the Pacific ENSO record.
Highlights
The Indian summer monsoon is the main driver of climate variability feeding the perennial streams of southern Asia and despite strong efforts still difficult to predict (Gadgil, 2003; Jayaraman, 2002)
Our results show that in summer, the south-eastward blowing Levar winds carry lithogenic matter, predominantly originating from Balochistan and the Sistan Basins, southward as dust to the northern Arabian Sea realm
River discharge is fed by humid air masses that are transported eastward from the Mediterranean and the Atlantic Ocean and vary in concert with the North Atlantic Oscillation (NAO) and El Niño Southern Oscillation (ENSO) due to associated changes in the configuration of the subtropical westerly jet (SWJ) stream over southwest Asia in winter
Summary
The Indian summer monsoon is the main driver of climate variability feeding the perennial streams of southern Asia and despite strong efforts still difficult to predict (Gadgil, 2003; Jayaraman, 2002). Northern Arabian Sea sediments are well known for their continuous seasonal varve-like lamination that is characterized by an alternation of dark and bright laminae with the potential of seasonally resolved paleo-reconstructions (Lückge et al, 2002; Von Rad et al, 2002b) Until now, these archives have been used to reconstruct sea surface temperatures and salinities (Böll et al, 2014; Doose-Rolinski et al, 2001; Munz et al, 2015), marine productivity (Böll et al, 2014; Von Rad et al, 1999a, 2002b), as well as inputs of pollen (Ivory and Lézine, 2009) and lithogenic matter from land (Lückge et al, 2001, 2002, 2012; Von Rad et al, 1999a, 2002b). These studies revealed strong teleconnections with North Atlantic climate variations reflecting, for example, Dansgaard–Oeschger and Heinrich events during the last glacial period (Deplazes et al, 2014; Reichart et al, 1997; Schulz et al, 1998)
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