ALBERT

Beschreibung: Coinciding with global warming, Arctic sea ice has rapidly decreased during the last four decades and climate scenarios suggest that sea ice may completely disappear during summer within the next about 50-100 years. Here we produce Arctic sea ice biomarker proxy records for the penultimate glacial (Marine Isotope Stage 6) and the subsequent last interglacial (Marine Isotope Stage 5e). The latter is a time interval when the high latitudes were significantly warmer than today. We document that even under such warmer climate conditions, sea ice existed in the central Arctic Ocean during summer, whereas sea ice was significantly reduced along the Barents Sea continental margin influenced by Atlantic Water inflow. Our proxy reconstruction of the last interglacial sea ice cover is supported by climate simulations, although some proxy data/model inconsistencies still exist. During late Marine Isotope Stage 6, polynya-type conditions occurred off the major ice sheets along the northern Barents and East Siberian continental margins, contradicting a giant Marine Isotope Stage 6 ice shelf that covered the entire Arctic Ocean.

Beschreibung: The simulation output of the stable water isotope enabled climate model ECHAM5/MPIOM-wiso is provided for time periods 130ka BP, 125 ka BP, and 120 ka BP. Boundary conditions for the simulations were provided by modified the greenhouse gas concentrations (available from ice core measurements) and the orbital configuration (calculated via the Berger solutions).

Beschreibung: This dataset contains results from simulations with the AWI Earth System Models AWI-ESM with two different model setups: one with an interactive ice sheet model (PISM) for the Greenland ice sheet domain and one without. With both model setups, the Representative Concentration Pathways scenarios RCP4.5 and RCP8.5 were simulated. The simulation runs were prolonged to the year 2200. We investigated the effect of the incorporated ice sheet model on the Atlantic meridional overturning circulation. As the ice sheet is not only melting but also growing in some areas, the freshwater release is partly compensated. Therefore, the effect on the Atlantic meridional overturning circulation is rather small. The dataset contains time series of global average temperature, atmospheric and oceanic freshwater fluxes for the Atlantic catchment area, several ice volume fluxes of the Greenland ice sheet, and the AMOC index. Furthermore, it contains spatial data mostly as anomalies (the last 30 year average minus the control state) of the Greenland ice sheet thickness and mass balance, sea surface salinity and sea ice concentration and precipitation minus evaporation and vertical profiles of anomalies of temperature, salinity, and density for the regions of deep water formation in the North Atlantic. All files are in the NetCDF format.

Beschreibung: Reconstructions of last interglacial (LIG, MIS 5e, ~127-117 ka) climate offer insights into the natural response and variability of the climate system during a period partially analogous to future climate change scenarios. We present well preserved fossil corals (Diploria strigosa) recovered from the southern Caribbean island of Bonaire (Caribbean Netherlands). These have been precisely dated by the 230Th/U-method to between 130 and 120 ka ago. Annual banding of the coral skeleton enabled construction of time windows of monthly resolved strontium/calcium (Sr/Ca) temperature proxy records. In conjunction with a previously published 118 ka coral record, our eight records of up to 37 years in length, cover a total of 105 years within the LIG period. From these, sea surface temperature (SST) seasonality and variability in the tropical North Atlantic Ocean is reconstructed. We detect similar to modern SST seasonality of ~2.9 °C during the early (130 ka) and the late LIG (120-118 ka). However, within the mid-LIG, a significantly higher than modern SST seasonality of 4.9 °C (at 126 ka) and 4.1 °C (at 124 ka) is observed. These findings are supported by climate model simulations and are consistent with the evolving amplitude of orbitally induced changes in seasonality of insolation throughout the LIG, irrespective of wider climatic instabilities that characterised this period. The climate model simulations suggest that the SST seasonality changes documented in our LIG coral Sr/Ca records are representative of larger regions within the tropical North Atlantic. These simulations also suggest that the reconstructed SST seasonality increase during the mid-LIG is caused primarily by summer warming. A 124 ka old coral documents, for the first time, evidence of decadal SST variability in the tropical North Atlantic during the LIG, akin to that observed in modern instrumental records.

Beschreibung: The seasonality of hydroclimate during past periods of warmer than modern global temperatures is a critical component for understanding future climate change scenarios. Although partially analogous to these scenarios, the last interglacial (LIG, Marine Isotope Stage 5e, ~127-117 ka) is a popular test-bed. We present coral d18O monthly resolved records from multiple Bonaire (southern Caribbean) fossil corals (Diploria strigosa) that date to between 130 and 118 ka. These records represent up to 37 years and cover a total of 105 years, offering insights into the seasonality and characteristics of LIG tropical Atlantic hydroclimate. Our coral d18O records and available coral Sr/Ca- sea surface temperature (SST) records reveal new insights into the variable relationship between the seasonality of tropical Atlantic seawater d18O (d18Oseawater) and SST. Coral d18O seasonality is found to coevolve with SST and insolation seasonality throughout the LIG, culminating in significantly higher than modern values at 124 and 126 ka. At 124 ka, we reconstruct a 2-month lead of the coral d18O vs. the Sr/Ca-SST annual cycle and increased d18Oseawater seasonality. A fully-coupled climate model simulates a concomitant increase of southern Caribbean Sea summer precipitation and depletion of summer d18Oseawater. LIG regional hydroclimate differed from today's semiarid climate with a minor rainy season during winter. Cumulatively our coral d18O, d18Oseawater and model findings indicate a mid-LIG northward expansion of the South American Intertropical Convergence Zone into the southern Caribbean Sea, highlighting the importance of regional aspects within reconstructions of LIG hydroclimate seasonality.

Beschreibung: We present basal melt rates for the ice shelves in equilibrium simulations of the Antarctic ice sheet (AIS), using the 3D thermodynamical Parallel Ice Sheet Model (PISM) version 1.1 with PICO as ocean component. The applied climate forcing consists of yearly mean present-day temperature and precipitation fields from RACMO2.3 (RACMO2 ANT27), and 400-800 m depth average ocean temperature and salinity, obtained from simulations using the atmosphere-ocean general circulation model COSMOS (ocean model MPIOM). COSMOS was run using pre-industrial settings (PID; 278 ppm CO2), settings from 40 kyr ago (40ka; 195 ppm CO2), and Last Glacial Maximum settings (LGM; 185 ppm CO2). All simulations are started with present-day bedrock conditions, and a present-day AIS size (Bedmap2). The steady state simulations are conducted by applying the same climate forcing over 200 kyr, after a thermodynamical spin-up (no mass changes) of 200,100 yr.

Beschreibung: Herein, we publish the simulated global annual mean surface air temperature (SAT), sea surface temperature (SST), sea surface salinity (SSS), sea ice cover (seaice), surface albedo (albedo) and total cloud cover (aclcov) over a time period of 100 years retrieved from equilibrium climate simulations for the Middle Miocene and Preindustrial. We simulate Miocene and Preindustrial climate states at different atmospheric CO2 concentrations. The model data has been used in the publication by Hossain et al., 2022. The climate data has been produced with AWI Earth System Model (AWI-ESM2.1; ECHAM6/JSBACH/MPIOM2/ OASIS3‐MCT), utilized at a spectral resolution of T63 (~1.88° x 1.88°) in the atmosphere with 47 vertical layers. FESOM2 uses the COREII mesh. The Miocene model setup is based on the combined high-resolution (0.1° x 0.1°) global bathymetry and topography (Middle Miocene; ~14 Ma) of Paxman et al. (2019), Hochmuth et al. (2020) and Straume et al. (2020). The model setup refers to boundary conditions (incl. changes in orography, bathymetry, physical land surface characteristics, ice sheets, atmospheric CO2) representative for the Miocene and Preindustrial. Details on setup and identifiers of Miocene and Preindustrial model simulations can be found in Table 1 of Hossain et al., 2022.

Beschreibung: This dataset contains the results of a simulation using the global climate model AWI-ESM coupled with the interactive ice sheet model PISM. The simulation consists of a historical run (1850-2014) and a future scenario using the Representative Concentration Pathways scenarios RCP8.5. This scenario spans the years 2006-2100 and was prolonged to the year 2299 with fixed greenhouse gas concentrations. The variables provided are temperature at 2 meters above surface and ice depth. The data are used for a mathematical model to describe long-term changes in extreme temperatures (Contzen, Dickhaus and Lohmann, 2023). This dataset contains spatial data on a regular lon lat grid (0.5°x0.5° horizontal resolution) using monthly time steps. All files are in the NetCDF format.