Gaudenz Deplazes

Weakening and strengthening of the Indian monsoon during Heinrich events and Dansgaard-Oeschger oscillations

The Dansgaard-Oeschger oscillations and Heinrich events described in North Atlantic sediments and Greenland ice are expressed in the climate of the tropics, for example, as documented in Arabian Sea sediments. Given the strength of this teleconnection, we seek to reconstruct its range of environmental impacts. We present geochemical and sedimentological data from core SO130-289KL from the Indus submarine slope spanning the last similar to 80 kyr. Elemental and grain size analyses consistently indicate that interstadials are characterized by an increased contribution of fluvial suspension from the Indus River. In contrast, stadials are characterized by an increased contribution of aeolian dust from the Arabian Peninsula. Decadal-scale shifts at climate transitions, such as onsets of interstadials, were coeval with changes in productivity-related proxies. Heinrich events stand out as especially dry and dusty events, indicating a dramatically weakened Indian summer monsoon, potentially increased winter monsoon circulation, and increased aridity on the Arabian Peninsula. This finding is consistent with other paleoclimate evidence for continental aridity in the northern tropics during these events. Our results strengthen the evidence that circum-North Atlantic temperature variations translate to hydrological shifts in the tropics, with major impacts on regional environmental conditions such as rainfall, river discharge, aeolian dust transport, and ocean margin anoxia. Key Points Intensity of Indian monsoon is traced with geochemical and grain size analyses of sediments Fluvial versus aeolian sediment input to Arabian Sea mimics DO oscillations During Heinrich events the Indian monsoon weakened distinctly

Impact of Indus River discharge on productivity and preservation of organic carbon in the Arabian Sea over the twentieth century

Marine high-productivity zones along the continents are of great economic importance, and they account for most organic carbon burial. The carbon cycle in many coastal zones is influenced by the sediments and dissolved nutrients introduced by rivers. However, there is little direct evidence for a regional marine response to changes in river dynamics. Here we present a suite of high-resolution records of organic and inorganic paleoceanographic proxies, which together demonstrate that past changes in Indus River discharge have strongly affected productivity patterns in the coastal northeastern Arabian Sea. Anthropogenic activity, including the building of dams and irrigation facilities during the past century, has drastically decreased the discharge rate of the Indus River. Between A.D. 1890 and 1998, the period over which this reduction occurred, primary productivity off the Pakistan coast seems to have decreased by more than one-third. Over the same period, the regional oxygen minimum zone weakened, increasing the supply of oxygen to the sediments, leaving the expected imprint on a suite of redox-sensitive elements and reducing the preservation of organic matter.