Periodic Reporting for period 1 - ELMO (Evolution of Low-latitude climates and Monsoon Onset)
Periodo di rendicontazione: 2021-09-01 al 2023-08-31
Changes in low-latitude sea surface temperature (SST) has far reaching consequences on Earth’s radiative budget, hydrological cycle, and ecosystems. Yet records of low-latitude SST during warmer-than-modern climates across the Cenozoic (0 – 60 million years ago (Ma)) remain limited. Further, the acquisition of accurate SST estimates in the geological past has inherent weaknesses with traditionally applied proxies for temperature reconstruction subject to both biological and geochemical caveats. This has often resulted in diverging absolute and relative SSTs, impacting our ability to constrain changes in meridional and zonal temperature gradients and corresponding climate feedbacks fundamental to better understanding both the influence and sensitivity of the low-latitudes to changing boundary conditions and global climate change.
Across the past decade there has been a concentrated effort to develop and apply clumped isotope thermometry as a viable approach for ocean temperature reconstruction from foraminifera. This approach is thought to be outwith biological vital effects and the requisite assumptions regarding past seawater chemistry due to the clumping of 13C-18O bonds being dictated, in isolation of seawater chemistry, by thermodynamics. Thus, one of the aims of ELMO is to apply this proxy approach to provide additional constraints on reconstructing past SST from a low-latitude site across the Cenozoic. To complement and better understand proxy reconstruction methods, ELMO will reconstruct Mg/Ca-temperatures, the traditional approach to temperature reconstruction using foraminifera shell geochemistry, to provide a direct comparison between temperatures derived from clumped isotope analysis. In addition to reconstructing a long-term SST record, the oceanographic conditions of the targeted site (IODP U1443, southern Bay of Bengal) are influenced by monsoonal forcing from the Indian Monsoon system. A secondary aim of ELMO is thus, to identify if any changes in temperature variability gained from individual foraminifera trace element analysis (Mg/Ca) using laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) can provide additional insights on the onset and evolution of the modern Indian Monsoon system.
Across the past decade there has been a concentrated effort to develop and apply clumped isotope thermometry as a viable approach for ocean temperature reconstruction from foraminifera. This approach is thought to be outwith biological vital effects and the requisite assumptions regarding past seawater chemistry due to the clumping of 13C-18O bonds being dictated, in isolation of seawater chemistry, by thermodynamics. Thus, one of the aims of ELMO is to apply this proxy approach to provide additional constraints on reconstructing past SST from a low-latitude site across the Cenozoic. To complement and better understand proxy reconstruction methods, ELMO will reconstruct Mg/Ca-temperatures, the traditional approach to temperature reconstruction using foraminifera shell geochemistry, to provide a direct comparison between temperatures derived from clumped isotope analysis. In addition to reconstructing a long-term SST record, the oceanographic conditions of the targeted site (IODP U1443, southern Bay of Bengal) are influenced by monsoonal forcing from the Indian Monsoon system. A secondary aim of ELMO is thus, to identify if any changes in temperature variability gained from individual foraminifera trace element analysis (Mg/Ca) using laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) can provide additional insights on the onset and evolution of the modern Indian Monsoon system.
ELMO was divided into the following 4 work packages: WP1 – Project Management, WP2 – Data Collection and Analysis, WP3 – Dissemination and WP4 – Outreach Activities. These work packages were constructed to ensure that integral to ELMO was both the development of the Fellow’s career and skillset whilst addressing the proposed scientific objectives. The fellow’s career development has greatly benefitted from activities undertaken within these different work packages.
WP2 of ELMO has produced long-term (0 – 60 Ma) clumped isotope-based temperature records from both planktic and benthic foraminifera from the tropical Indian Ocean (IODP Site U1443 and ODP Site 757). The approach to target benthic foraminifera for analysis was an addition to the project following the reconstruction of erroneously cold temperatures from the planktic foraminifera, suggesting a heightened diagenetic sensitivity of clumped isotope thermometry within planktic foraminifera. The deep-water temperatures reconstructed from benthic foraminifera permitted a means to estimate the fraction of diagenetic calcite and overprinting present within the analysed planktic foraminifera using end-member modelling. This provided an assessment of differences in carbonate precipitation settings, between the upper mixed layer with bottom waters, throughout the studied interval. In combination with clumped isotope analysis, planktic foraminifera specimens were analysed using LA-ICP-MS to obtain SST estimates from Mg/Ca ratios. Individual foraminifera analysis was undertaken on discrete populations from the mid-Miocene through to Pleistocene (0 – 15 Ma) providing both a contemporaneous SST record to compare with clumped isotope-based temperatures whilst also providing information on changes in temperature variability. Additionally, through collaboration, a low-resolution temperature record from organic biomarker geochemical methods has been produced to further disentangle proxy divergences. Three publications are in preparation.
WP2 of ELMO has produced long-term (0 – 60 Ma) clumped isotope-based temperature records from both planktic and benthic foraminifera from the tropical Indian Ocean (IODP Site U1443 and ODP Site 757). The approach to target benthic foraminifera for analysis was an addition to the project following the reconstruction of erroneously cold temperatures from the planktic foraminifera, suggesting a heightened diagenetic sensitivity of clumped isotope thermometry within planktic foraminifera. The deep-water temperatures reconstructed from benthic foraminifera permitted a means to estimate the fraction of diagenetic calcite and overprinting present within the analysed planktic foraminifera using end-member modelling. This provided an assessment of differences in carbonate precipitation settings, between the upper mixed layer with bottom waters, throughout the studied interval. In combination with clumped isotope analysis, planktic foraminifera specimens were analysed using LA-ICP-MS to obtain SST estimates from Mg/Ca ratios. Individual foraminifera analysis was undertaken on discrete populations from the mid-Miocene through to Pleistocene (0 – 15 Ma) providing both a contemporaneous SST record to compare with clumped isotope-based temperatures whilst also providing information on changes in temperature variability. Additionally, through collaboration, a low-resolution temperature record from organic biomarker geochemical methods has been produced to further disentangle proxy divergences. Three publications are in preparation.
ELMO has produced three key records: a long-term planktic and benthic clumped isotope record and a Mg/Ca-SST record from individual foraminifera populations from 0 – 15 Ma.
There remain limited ocean temperature records produced from clumped isotope analysis of foraminifera and is growing in popularity owing to its independence from vital and biological effects. However, the results from ELMO show that the application of this proxy method requires careful curation owing to the diagenetic sensitivity found in planktic foraminifera compared to that gained from “traditional” Mg/Ca analysis. This will be directly relevant to informing the paleoclimate community of the limitations of this new proxy approach. Combined, the newly produced records deliver advances in our understanding to temperature reconstruction.
ELMO has produced the first long-term deep ocean temperature record from the tropical Indian Ocean across the Cenozoic. In addition, the clumped isotope temperatures coupled with the benthic 18O values provides a means to reconstruct deep ocean 18Osw, providing information on Cenozoic ice sheet evolution when compared with benthic 18Osw from other ocean basins. This record will be invaluable in contributing to our understanding of the evolution of deep ocean temperatures across the Cenozoic, water mass routing in response to large-scale changes in boundary conditions and further expand on understanding benthic foraminifera 18O signals.
The discrete populations of individually analysed foraminifera from the mid-Miocene through to the Pleistocene provide potential insights into the evolution of the modern Indian Monsoon system owing to reconstructed changes in the temperature variance gained from analysis of discrete foraminifera populations across the studied interval.
There remain limited ocean temperature records produced from clumped isotope analysis of foraminifera and is growing in popularity owing to its independence from vital and biological effects. However, the results from ELMO show that the application of this proxy method requires careful curation owing to the diagenetic sensitivity found in planktic foraminifera compared to that gained from “traditional” Mg/Ca analysis. This will be directly relevant to informing the paleoclimate community of the limitations of this new proxy approach. Combined, the newly produced records deliver advances in our understanding to temperature reconstruction.
ELMO has produced the first long-term deep ocean temperature record from the tropical Indian Ocean across the Cenozoic. In addition, the clumped isotope temperatures coupled with the benthic 18O values provides a means to reconstruct deep ocean 18Osw, providing information on Cenozoic ice sheet evolution when compared with benthic 18Osw from other ocean basins. This record will be invaluable in contributing to our understanding of the evolution of deep ocean temperatures across the Cenozoic, water mass routing in response to large-scale changes in boundary conditions and further expand on understanding benthic foraminifera 18O signals.
The discrete populations of individually analysed foraminifera from the mid-Miocene through to the Pleistocene provide potential insights into the evolution of the modern Indian Monsoon system owing to reconstructed changes in the temperature variance gained from analysis of discrete foraminifera populations across the studied interval.