Holocene tropical western Indian Ocean sea surface temperatures in covariation with climatic changes in the Indonesian region

• Published in: Paleoceanography 2014-05, Vol.29 (5), p.423-437
• Main Authors: Kuhnert, Henning, Kuhlmann, Holger, Mohtadi, Mahyar, Meggers, Helge, Baumann, Karl-Heinz, Pätzold, Jürgen
• Format: Article
• Language: English
• Subjects: Air temperature; Climate change; Cooling; Foraminifera; Global climate; Holocene; Indian Ocean; Marine; Mg/Ca; Ocean temperature; Paleoclimate science; Sea surface temperature; Thermocline; Upwelling
• ISSN: 0883-8305; 2572-4517; 1944-9186; 2572-4525
• DOI: 10.1002/2013PA002555

The sea surface temperature (SST) of the tropical Indian Ocean is a major component of global climate teleconnections. While the Holocene SST history is documented for regions affected by the Indian and Arabian monsoons, data from the near‐equatorial western Indian Ocean are sparse. Reconstructing past zonal and meridional SST gradients requires additional information on past temperatures from the western boundary current region. We present a unique record of Holocene SST and thermocline depth variations in the tropical western Indian Ocean as documented in foraminiferal Mg/Ca ratios and δ18O from a sediment core off northern Tanzania. For Mg/Ca and thermocline δ18O, most variance is concentrated in the centennial to bicentennial periodicity band. On the millennial time scale, an early to mid‐Holocene (~7.8–5.6 ka) warm phase is followed by a temperature drop by up to 2°C, leading to a mid‐Holocene cool interval (5.6–4.2 ka). The shift is accompanied by an initial reduction in the difference between surface and thermocline foraminiferal δ18O, consistent with the thickening of the mixed layer and suggestions of a strengthened Walker circulation. However, we cannot confirm the expected enhanced zonal SST gradient, as the cooling of similar magnitude had previously been found in SSTs from the upwelling region off Sumatra and in Flores air temperatures. The SST pattern probably reflects the tropical Indian Ocean expression of a large‐scale climate anomaly rather than a positive Indian Ocean Dipole‐like mean state. Key Points Holocene tropical western Indian Ocean surface temperatures changed markedly Mid‐Holocene cooling parallels Eastern Indian Ocean temperature decline Pronounced centennial‐scale SST variability present