Description: Indian Ocean surface circulation is an important part of the global ocean conveyor belt, and is connected via two important gateways including the Indonesian Throughflow, and the Agulha Leakage. Changes in the surface hydrography of the Indian Ocean may therefore impact on the global overturning circulation. Using planktonic foraminifera-based reconstructions of Indian Ocean surface salinity and temperature, we find that Indian Ocean surface water salinify during glacial intensification. Here we present reconstructions of global mean sea level using the ice sheet model ANICE and benthic foraminifera oxygen isotope data from U1476 to analyse changes in mean global sea level and calculate whole ocean changes in seawater oxygen isotopes. We use this information to show that the Indian Ocean surface hydrography changed in different ways from other ocean basins during Late Pleistocene glacial-interglacial cycles.

Description: Indian Ocean surface circulation is an important part of the global ocean conveyor belt, and is connected via two important gateways including the Indonesian Throughflow, and the Agulhas Leakage. Changes in the surface hydrography of the Indian Ocean may therefore impact on the global overturning circulation. Using planktonic foraminifera-based reconstructions of Indian Ocean surface salinity and temperature, we find that Indian Ocean surface water became saliter during glacial intensification. Here we present bathymetrical change data for the Indonesian Archipelago which shows that the Indonesian Throughflow was likely impacted due to changes in global mean sea level and possibly drove the changes in salinity during a glacial cycle.

Description: Indian Ocean surface circulation is an important part of the global ocean conveyor belt, and is connected via two important gateways including the Indonesian Throughflow, and the Agulha Leakage. Changes in the surface hydrography of the Indian Ocean may therefore impact on the global overturning circulation. Here we present planktonic foraminifera-based stack of oxygen isotopes as proxy for surface salinity from the surface Indian Ocean. We find that Indian Ocean surface salinity (along with temperature) increases during glacial intensification. We link this phenomenon to dynamics in the Indonesian Archipelago.

Description: Indian Ocean surface circulation is an important part of the global ocean conveyor belt, and is connected via two important gateways including the Indonesian Throughflow, and the Agulha Leakage. Changes in the surface hydrography of the Indian Ocean may therefore impact on the global overturning circulation. Here we present oxygen-isotopes and magnesium/calcium ratios from planktic foraminifer Globigernoides ruber from core site U1476 to reconstruct sea surface salinity and sea surface temperature in the Mozambique Channel, Indian Ocean for the past 1.2Ma. We investigated the changes in the surface hydrography of the Mid-to-Late Pleistocene and find an early salinification and warming during glacial cycles.

Description: Indian Ocean surface circulation is an important part of the global ocean conveyor belt, and is connected via two important gateways including the Indonesian Throughflow, and the Agulha Leakage. Changes in the surface hydrography of the Indian Ocean may therefore impact on the global overturning circulation. Here we present spectral, and cross spectral analysis results which show that Indian Ocean surface salinity and temperature increased during glacial intensification, with a significant lag prior to deglaciations.

Description: The confidence intervals published here are supporting and complementing the spectral and cross spectral data under: doi:10.1594/PANGAEA.955738.

Description: This dataset explores the variability in glacial-interglacial surface hydrography in the western Indian Ocean across the middle to late Pleistocene. Here, we provide 1kyr resolution Mg/Ca-based sea surface temperatures and surface oxygen isotope ratios of seawater (ice volume corrected) as proxy for surface palaeo-salinity from surface dwelling foraminifera Globigerinoides ruber from International Ocean Discovery Program core site U1476 located in the Mozambique Channel, which we use in combination with other records to create Indian Ocean sea surface salinity and sea surface temperature stacks. The data show increases in sea surface temperature and salinity during glaciation, with maximum temperature and salinity occurring at glacial maxima, prior to global deglaciations as indicated by benthic oxygen isotopes, a proxy for global ice volume. Lead-lag analyses were conducted using cross-spectral analysis between sea surface temperatures, salinity, and benthic oxygen isotopes. In parallel, sea-to-land pixel ratios from the ANICE-SELEN model across the Indonesian Archipelago show changes in land surfacing in the Indonesian archipelago due to globally sinking sea levels. The increase in surface temperature and salinification at U1476 occurs at the same time as major land surfacing in the Indonesian Archipelago suggesting a mechanistical link between land surfacing due to global sea level lowering, and changes in Indian Ocean surface hydrography that appears to be a resulting reduction in the considerably fresher Indonesian throughflow entering the Indian Ocean.

Description: Interactions between midlatitude westerlies and the Pamir–Tian Shan mountains significantly impact hydroclimate patterns in Central Asia today, and they played an important role in driving Asian aridification during the Cenozoic. We show that distinct westeast hydroclimate differences were established over Central Asia during the late Oligocene (ca. 25 Ma), as recorded by stable oxygen isotopic values of soil carbonates. Our climate simulations show that these differences are present when relief of the Pamir–Tian Shan is higher than 75% of modern elevation (∼3000 m). Integrated with geological evidence, we suggest that a significant portion of the Pamir–Tian Shan orogen had reached elevations of ∼3 km and acted as a moisture barrier for the westerlies since ca. 25 Ma.

Description: Numerical simulations employing prognostic sta- ble water isotopes can not only facilitate our understanding of hydrological processes and climate change but also al- low for a direct comparison between isotope signals obtained from models and various archives. In the current work, we describe the performance and explore the potential of a new version of the Earth system model AWI-ESM (Alfred We- gener Institute Earth System Model), labeled AWI-ESM-2.1- wiso, in which we incorporated three isotope tracers into all relevant components of the water cycle. We present here the results of pre-industrial (PI) and mid-Holocene (MH) simula- tions. The model reproduces the observed PI isotope compo- sitions in both precipitation and seawater well and captures their major differences from the MH conditions. The sim- ulated relationship between the isotope composition in precipitation (d18Op) and surface air temperature is very similar between the PI and MH conditions, and it is largely consis- tent with modern observations despite some regional model biases. The ratio of the MH–PI difference in δ18Op to the MH–PI difference in surface air temperature is comparable to proxy records over Greenland and Antarctica only when summertime air temperature is considered. An amount effect is evident over the North African monsoon domain, where a negative correlation between δ18Op and the amount of pre- cipitation is simulated. As an example of model applications, we studied the onset and withdrawal date of the MH West African summer monsoon (WASM) using daily variables. We find that defining the WASM onset based on precipitation alone may yield erroneous results due to the substantial daily variations in precipitation, which may obscure the dis- tinction between pre-monsoon and monsoon seasons. Com- bining precipitation and isotope indicators, we suggest in this work a novel method for identifying the commencement of the WASM. Moreover, we do not find an obvious difference between the MH and PI periods in terms of the mean onset of the WASM. However, an advancement in the WASM with- drawal is found in the MH compared to the PI period due to an earlier decline in insolation over the northern location of Intertropical Convergence Zone (ITCZ).

Description: The last deglaciation was characterized by a sequence of abrupt climate events thought to be linked to rapid changes in Atlantic meridional overturning circulation (AMOC). The sequence includes a weakening of the AMOC after the Last Glacial Maximum (LGM) during Heinrich Stadial 1 (HS1), which ends with an abrupt AMOC amplification at the transition to the Bølling/Allerød (B/A). This transition occurs despite persistent deglacial meltwater fluxes that counteract vigorous North Atlantic deep-water formation. Using the Earth system model COSMOS with a range of deglacial boundary conditions and reconstructed deglacial meltwater fluxes, we show that deglacial CO2 rise and ice sheet decline modulate the sensitivity of the AMOC to these fluxes. While declining ice sheets increase the sensitivity, increasing atmospheric CO2 levels tend to counteract this effect. Therefore, the occurrence of a weaker HS1 AMOC and an abrupt AMOC increase in the presence of meltwater, might be explained by these effects, as an alternative to or in combination with changes in the magnitude or routing of meltwater discharge.