DOI: 10.5061/dryad.rfj6q57mn
title: Past intrusion of circumpolar deep water in the Ross Sea: Impacts on the ancient Ross Ice Shelf

description: The Ross Ice Shelf, Antarctica's largest by surface area, may face
 increased instability with future warming, posing a significant threat to
 the stability of the Antarctic Ice Sheet. Understanding the dynamics
 driving its retreat during past warming events is crucial for predicting
 future sea-level rise. Here, we present a multi-proxy record that
 comprehensively reconstructs the paleoenvironmental conditions of the
 ocean and cryosphere in the Ross Sea during the last 40,000 years. Our
 results accurately demonstrate the intrusion of warm Circumpolar Deep
 Water in the JOIDES trough (western Ross Sea) and the embayment of the
 ancestral ice shelf edge shortly after the end of the Last Glacial
 Maximum. The oceanic warming documented in the Ross Sea closely aligns
 with the southward migration of the westerly and easterly winds. This
 suggests a common, large-scale mechanism driving changes across the
 Pacific sector of the Southern Ocean, echoing on the continental margin.
 Our study disentangles the complex interactions between the atmosphere,
 ocean, and cryosphere that reduced the ice shelf extent since the onset of
 the last deglaciation, potentially facilitating Marine Ice Sheet
 Instability.
description: # Past intrusion of circumpolar deep water in the Ross Sea: Impacts on the
 ancient Ross Ice Shelf
 [https://doi.org/10.5061/dryad.rfj6q57mn](https://doi.org/10.5061/dryad.rfj6q57mn) ## Description of the data and file structure #### Overview This dataset contains multi-proxy sediment core data collected for paleoenvironmental reconstruction. In paleoclimatology and paleoceanography, proxies are indirect measures used to reconstruct past environmental conditions. Since we cannot directly observe ancient climates or ecosystems, we rely on chemical, biological, or physical signals preserved in natural archives, such as sediment cores, to infer parameters like temperature, sea ice extent, productivity, and ocean circulation. **Biomarkers** like IPSO25 or brassicasterol reflect the presence of certain algae linked to sea-ice conditions or productivity. **Isotopic ratios** (e.g., δ13C) provide insights into carbon sources and biogeochemical cycling. The **RI-OH'** proxy is a relatively recent organic geochemical tool used to reconstruct sea water temperatures. It is derived from specific lipids produced by marine archaea. Among various paleotemperature proxies (such as TEX86 or U37K'), RI-OH' is particularly well-suited for application in **polar regions**, where other proxies may be less reliable. **Elemental ratios** (e.g., Zr/Rb) and **magnetic susceptibility** indicate sediment origin and transport processes and reflect the grain size of the core. Ice-rafted debris (IRDs) assess iceberg activity and glacial dynamics. **Foraminifera** are calcareous microfossils commonly preserved in marine sediment cores. Their presence, abundance, and assemblage composition provide valuable insights into the paleoenvironmental evolution of specific regions. These proxies are interpreted using modern analogs and experimental calibrations, and when **combined**, offer a powerful multi-proxy approach to reconstruct past environmental variability. The data is organized across five sheets, each representing a distinct analytical dataset. The sheets include organic geochemistry, elemental ratios, IRDs, microfossils, and physical properties. All data are organized with age or depth as reference. --- ### Sheet 1-organic proxies: **Geochemical and Biomarker Data** | Variable | Unit | Description | | :---------------------- | :------------------- | :------------------------------------------------------------------------------------ | | **Ages (yr BP)** | Years Before Present | Calibrated age in years before present (0 = 1950 AD). | | **DBD (g/cm³)** | g/cm³ | Dry Bulk Density of the sediment. | | **Sed rate (cm/yr)** | cm/year | Sedimentation rate at each depth. | | **TOC (%)** | % | Total Organic Carbon content, indicating organic matter preservation. | | **TN (%)** | % | Total Nitrogen content. | | **δ13C (‰)** | per mil (‰) | Carbon isotopic composition, indicative of organic matter sources. | | **Diene (IPSO25)** | ng/g sediment | Biomarker used to infer past sea-ice and fast-ice conditions. | | **Triene a / Triene b** | ng/g sediment | open marine diatoms related biomarkers. | | **Brassicasterol** | µg/g sediment | Biomarker associated with diatom productivity. | | **IPSO flux** | ng/cm²\*year | Flux of IPSO25 biomarker, normalized to sedimentation rate. | | **Triene flux** | ng/cm²\*year | Flux of combined triene biomarkers. | | **Brassicasterol flux** | µg/cm²\*year | Flux of brassicasterol. | | **Ri-OH (SOT °C)** | °C | Subsurface Ocean Temperature (SOT) inferred from Ri-OH proxy, obtained from OH-GDGTs. | | **Error (Ri-OH) (°C)** | °C | Uncertainty associated with SOT estimates. | --- ### Sheet 2-XRF: **Elemental Ratio** | Variable | Unit | Description | | :-------------- | :------------------- | :------------------------------------------------------------------------------------------------ | | **Age (yr BP)** | Years Before Present | Calibrated age. | | **ln(Zr/Rb)** | log ratio | Natural logarithm of the Zirconium to Rubidium ratio — proxy for grain size or terrigenous input. | --- ### Sheet 3: **Ice-Rafted Debris (IRD)** | Variable | Unit | Description | | :-------------- | :------------------- | :------------------------------------------------------------------------------------------------ | | **Age (yr BP)** | Years Before Present | Calibrated age. | | **IRDs (wt.%)** | % by weight | Proportion of Ice-Rafted Debris in the sediment, indicating iceberg activity or glacial dynamics. | --- ### Sheet 4: **Foraminifera and Sub-Ice Shelf Assemblages** | Variable | Unit | Description | | :-------------------- | :------------------- | :--------------------------------------------------------------------------------------------------------------------- | | **Ages (yr BP)** | Years Before Present | Calibrated age. | | **Depth (cm bsf)** | cm below seafloor | Depth of the sediment sample. | | **Sub ice shelf FA** | n/gr sediment | Abundance of foraminiferal assemblages associated with sub-ice shelf environments. | | **Trifarina spinosa** | n/gr sediment | Counts of *Trifarina earlandi with spines*, a benthic foraminifera species used in high-energy environmental settings. | --- ### Sheet 5: **Physical Properties** | Variable | Unit | Description | | :-------------------------- | :---------------- | :---------------------------------------------------------------------------------------------------------------------------------------------- | | **Depth (cm bsf)** | cm below seafloor | Sample depth. | | **Magnetic Susceptibility** | x10⁻⁵ SI | Proxy for mineral content, especially terrigenous (magnetic) input. Higher values often indicate higher sedimentation from continental sources. | --- ### Notes for Users * All ages are provided in calibrated years before present (BP), with 0 BP = 1950 CE. * Where applicable, fluxes are calculated by combining concentrations with sedimentation rates and dry bulk density. * Some proxy interpretations (e.g., IPSO25, Ri-OH) are based on published calibration methods. Users are encouraged to consult the associated publications for methodological details.  * IPSO 25: doi.org/10.1038/ncomms12655 * GDGTs: doi.org/10.1029/2023GL103109 * Graisize proxy for the Ross Sea: doi.org/10.1029/2020GC009350 ## Code/software The dataset is in .xls so can be ready by any Microsoft Excel, Google Sheets, LibreOffice Calc, Apple Numbers and similar.  ## Access information Other publicly accessible locations of the data: * n/a Data was derived from the following sources: * n/a