An official website of the United States government
Abstract Reconstructing the history of polar temperature from ice core water isotope (δ18O) calibration has remained a challenge in paleoclimate research, because of our incomplete understanding of various temperature–δ18O relationships. This paper resolves this classical problem in a new framework called the unified slope equations (USE), which illustrates the general relations among spatial and temporalδ18O–surface temperature slopes. The USE is applied to the Antarctica temperature change during the last deglaciation in model simulations and observations. It is shown that the comparable Antarctica-mean spatial slope with deglacial temporal slope inδ18O–surface temperature reconstruction is caused, accidentally, by the compensation responses between theδ18O–inversion layer temperature relation and the inversion layer temperature itself. Furthermore, in light of the USE, we propose that the present seasonal slope ofδ18O–inversion layer temperature is an optimal paleothermometer that is more accurate and robust than the spatial slope. This optimal slope suggests the possibility of reconstructing past Antarctic temperature changes using present and future instrumental observations. Significance StatementThis paper develops a new framework called the unified slope equations (USE) to provide, for the first time, a general relation among various spatial and temporal water isotope–temperature slopes. The application of the USE to Antarctic deglacial temperature change shows that the optimal paleothermometer is the seasonal slope of the inversion layer temperature.
more »
« less
Response of Water Isotopes in Precipitation to a Collapse of the West Antarctic Ice Sheet in High-Resolution Simulations with the Weather Research and Forecasting Model
Abstract The West Antarctic Ice Sheet (WAIS) may have collapsed during the last interglacial period, between 132 000 and 116 000 years ago. The changes in topography resulting from WAIS collapse would be accompanied by significant changes in Antarctic surface climate, atmospheric circulation, and ocean conditions. Evidence of these changes may be recorded in water-isotope ratios in precipitation archived in the ice. We conduct high-resolution simulations with an isotope-enabled version of the Weather Research and Forecasting Model over Antarctica, with boundary conditions provided by climate model simulations with both present-day and lowered WAIS topography. The results show that while there is significant spatial variability, WAIS collapse would cause detectable isotopic changes at several locations where ice-core records have been obtained or could be obtained in the future. The most robust signals include elevatedδ18O at SkyTrain Ice Rise in West Antarctica and elevated deuterium excess andδ18O at Hercules Dome in East Antarctica. A combination of records from multiple sites would provide constraints on the timing, rate, and magnitude of past WAIS collapse.
more »
« less
- PAR ID:
- 10431621
- Publisher / Repository:
- American Meteorological Society
- Date Published:
- Journal Name:
- Journal of Climate
- Volume:
- 36
- Issue:
- 16
- ISSN:
- 0894-8755
- Page Range / eLocation ID:
- p. 5417-5430
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Abstract Earth's orbital geometry exerts a profound influence on climate by regulating changes in incoming solar radiation. Superimposed on orbitally paced climate change, Pleistocene records reveal substantial millennial‐scale variability characterized by abrupt changes and rapid swings. However, the extent to which orbital forcing modulates the amplitude and timing of these millennial variations is unclear. Here we isolate the magnitude of millennial‐scale variability (MMV) in two well‐dated records, both linked to precession cycles (19,000‐ and 23,000‐year periodicity): composite Chinese speleothemδ18O, commonly interpreted as a proxy for Asian monsoon intensity, and atmospheric methane. At the millennial timescale (1,000–10,000 years), we find a fundamental decoupling wherein precession directly modulates the MMV of methane but not that of speleothemδ18O, which is shown to be strikingly similar to the MMV of Antarctic ice coreδ2H. One explanation is that the MMV of methane responds to changes in midlatitude to high‐latitude insolation, whereas speleothemδ18O is modulated by internal climate feedbacks.more » « less
-
Observational evidence indicates that the West Antarctic Ice Sheet (WAIS) is losing mass at an accelerating rate. Impacts to global climate resulting from changing ocean circulation patterns due to increased freshwater runoff from Antarctica in the future could have significant implications for global heat transport, but to-date this topic has not been investigated using complex numerical models with realistic freshwater forcing. Here, we present results from a high resolution fully coupled ocean-atmosphere model (CESM 1.2) forced with runoff from Antarctica prescribed from a high resolution regional ice sheet-ice shelf model. Results from the regional simulations indicate a potential freshwater contribution from Antarctica of up to 1 m equivalent sea level rise by the end of the century under RCP 8.5 indicating that a substantial input of freshwater into the Southern Ocean is possible. Our high resolution global simulations were performed under IPCC future climate scenarios RCP 4.5 and 8.5. We will present results showing the impact of WAIS collapse on global ocean circulation, sea ice, air temperature, and salinity in order to assess the potential for abrupt climate change triggered by WAIS collapse.more » « less
-
Abstract Eocene climate cooling, driven by the fallingpCO2and tectonic changes in the Southern Ocean, impacted marine ecosystems. Sharks in high‐latitude oceans, sensitive to these changes, offer insights into both environmental shifts and biological responses, yet few paleoecological studies exist. The Middle‐to‐Late Eocene units on Seymour Island, Antarctica, provide a rich, diverse fossil record, including sharks. We analyzed the oxygen isotope composition of phosphate from shark tooth bioapatite (δ18Op) and compared our results to co‐occurring bivalves and predictions from an isotope‐enabled global climate model to investigate habitat use and environmental conditions. Bulk δ18Opvalues (mean 22.0 ± 1.3‰) show no significant changes through the Eocene. Furthermore, the variation in bulk δ18Opvalues often exceeds that in simulated seasonal and regional values. Pelagic and benthic sharks exhibit similar δ18Opvalues across units but are offset relative to bivalve and modeled values. Some taxa suggest movements into warmer or more brackish waters (e.g.,Striatolamia,Carcharias) or deeper, colder waters (e.g.,Pristiophorus). Taxa likeRajaandSqualusdisplay no shift, tracking local conditions in Seymour Island. The lack of difference in δ18Opvalues between pelagic and benthic sharks in the Late Eocene could suggest a poorly stratified water column, inconsistent with a fully opened Drake Passage. Our findings demonstrate that shark tooth bioapatite tracks the preferred habitat conditions for individual taxa rather than recording environmental conditions where they are found. A lack of secular variation in δ18Opvalues says more about species ecology than the absence of regional or global environmental changes.more » « less
-
Abstract The fate of the West Antarctic Ice Sheet (WAIS)1is the largest cause of uncertainty in long-term sea-level projections. In the last interglacial (LIG) around 125,000 years ago, data suggest that sea level was several metres higher than today2–4, and required a significant contribution from Antarctic ice loss, with WAIS usually implicated. Antarctica and the Southern Ocean were warmer than today5–8, by amounts comparable to those expected by 2100 under moderate to high future warming scenarios. However, direct evidence about the size of WAIS in the LIG is sparse. Here we use sea salt data from an ice core from Skytrain Ice Rise, adjacent to WAIS, to show that, during most of the LIG, the Ronne Ice Shelf was still in place, and close to its current extent. Water isotope data are consistent with a retreat of WAIS9, but seem inconsistent with more dramatic model realizations10in which both WAIS and the large Antarctic ice shelves were lost. This new constraint calls for a reappraisal of other elements of the LIG sea-level budget. It also weakens the observational basis that motivated model simulations projecting the highest end of projections for future rates of sea-level rise to 2300 and beyond.more » « less
