Funds are provided for the continued development and testing of a new technique for acquiring reliable delta 18O data from slightly to moderately altered planktic shells preserved in deep-sea sediments. This technique uses a secondary ion mass spectrometer (SIMS) for in situ delta 18O analysis of domains within individual planktic shells recovered from Early Paleogene deep-sea records. Initial results confirm the veracity of this approach suggesting that it will be transformative for quantifying and circumventing the effects of diagenesis on 18O obtained from planktic shells. Paired delta 18O values with Mg/Ca ratios in the same planktic shell will be used to reconstruct Early Paleogene variation in SSTs and seawater delta 18O at tropical (Site 865) and subpolar (Site 690) latitudes. The basal areas of pustular outgrowths (muricae) on their chamber walls represent domains of enhanced biocalcification that contain no mural pores, making them less susceptible to diagenesis and ideal targets for SIMS. Objectives of this proposal are threefold: (1) Reassess tropical open-ocean SSTs during the Early Paleogene. (2) Quantify the effects of diagenesis on paleoceanographic proxies. (3) Compare low- and high-latitude records with emphasis on transient hyperthermal climate states.
Broader Impacts: The method, when widely applicable, could transform the study of paleoclimates based of planktic foraminiferal delta 18O. The study of Early Paleogene greenhouse climate could be an analog for future climate change driven by fossil fuel emissions.
Background: Planktonic foraminifera (forams) are unicellular marine organisms that populate the modern ocean and have a rich fossil record that spans the past 150 million years of Earth history. These amoeboid protists grow tiny shells (<1 mm) that are composed of the mineral calcite (CaCO3). Upon death, their calcite shells sink down into the ocean interior where they are deposited on the seafloor and accummulate into one of the most complete and detailed fossil records of past ocean-climate change. Owing to their shear numeric abundances in marine sediments, foram shells are routinely used to construct geochemical records expressing past ocean-climate change; hence, these tiny microfossils are often referred to as "the ocean's story tellers". However, it has long been suspected that original chemistries of foram shells are not preserved owing to the likelihood of post-mortem chemical alteration by various processes operating on the seafloor within the sediments; a post-depositional process of chemical alteration called diagenesis. Intellectual Merit: NSF funds (Award #1131516) were used to develop a new analytical technique that enables researchers to identify and measure the chemical compositions of minute domains (3 to 10 micrometer spots) within an individual foram shell, making it possible to identify (and avoid) subdomains within foram shells that have been chemically altered by diagenetic processes. Thus, this pioneering advance enables researchers to generate geochemcial records that more faithfully reflect such aspects of past surface-ocean conditions as temperature and salinity. Application of this novel (state-of-the-art) analytical technique to remove the bias imposed by diagenesis and measure the original chemistries of fossil forams preserved in deep-sea sediments is greatly enhancing the fidelity of foram-based geochemical records of past greenhouse climate states. This technological breakthrough is important because it resolves discrepancies between climate-model predictions and the published data. Specifically, previoiusly published foram-based geochemical records for past greenhouse climate states are typified by amplified polar warming with little, to no, warming in the tropics. This latitudinal gradient in sea-surface temperatures is incompatible with climate-model simulations, and the resulting data/model mismatch has been referred to as the "cool tropics paradox". Resolution of the cool tropics paradox is important because the particular greenhouse climate state herein studied is widely touted as being an ancient analog for future global warming driven by anthropogenic carbon input. Results: Salient findings of our research are (1) tropical sea-surfaces temperatures (~33ºC) were about ~6ºC warmer than indicated by previously published records for this ancient greenhouse climate state and (2) the tropical component (Hadley Cell) of the global hydrologic cycle was profoundly perturbed resulting in vigorous poleward transport of water vapor during this ancient episode of global warming. Broader Impacts: The findings of our research are generally consonant with climate-model predictions, and have important societal impacts. Water is the lifeblood of our planet, but it also plays an instrumental role in climate as it is an important greenhouse gas and since latitudinal (tropical-to-polar) transport of atmospheric water vapor balances Earth's energy budget by redistributing heat across the planet. With this in mind, the evidence provided by our research indicates that tropical regions will become progressively wetter with increased storm intensity as surface temperatures continue to rise in the future. Moreover, our results refute the erronenous notion that tropical temperatures have remained relatively constant over time due to a hypothetical "thermostatic mechanism". The new records of ocean-climate change that we are generating provide a more robust database that will enable governmental agencies to make more informed decisions regarding legislation that affects societal and industrial practices. Aside from the scientific achievements, we note that the lion's share of these monies were used to help pay infrastructural costs of a public university, and support/train a promising, young research scientist that is now based at Rutgers University.
