Foraminifers (Benthic)

Binczewska, Anna; Asteman, Irina Polovodova; Farmer, Elizabeth J.

doi:10.1007/978-94-007-6644-0_60-1

Cited by 1 publication

(1 citation statement)

References 29 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Within marine archives, foraminifera, which inhabited the ocean for more than 500 million years (BouDagher-Fadel, 2008), have gained considerable attention and have been widely assessed for palaeoclimatic reconstruction. Foraminifer is a cell organism encased by a shell (test) that can be classified as either calcareous (composed of CaCO3), arenaceous (built of sediment particles), or organic (made of tectin), with calcareous foraminifera being the most abundant due to its good preservation potential and greater diversity (Binczewskaa et al, 2015). Foraminifera are primarily categorised into three groups: i) planktonic, ii) smaller benthic, and iii) the larger benthic (distinguished as a different group due to their larger size and complex interior) (Boersma, 1998).…”

Section: Foraminifera: Marine Archives For Palaeoclimatic Reconstructionmentioning

confidence: 99%

Long-term variability of ocean chemistry : implications for deep-time palaeothermometry and the carbon cycle

Nambiar

View full text Add to dashboard Cite

While high-quality climate reconstructions of some past warm periods in the Cenozoic era now exist, the geological processes responsible for driving the observed longterm changes in atmospheric CO2 are not sufficiently well understood. The long-term change in atmospheric CO2 across the Cenozoic has been proposed to be driven by processes such as terrestrial weathering, organic carbon production and burial, reverse weathering, and volcanic degassing. One way of constraining the relative importance of the various driving forces proposed so far is to better understand the degree to which ocean chemistry has changed because the chemistry of seawater responds to geologic processes that drive atmospheric CO2. In addition, knowledge of the concentration of the major elements in seawater is crucial for accurately applying proxies such as those based on the boron isotopic composition and Mg/Ca of marine carbonates (a proxy for palaeo pH/CO2 and palaeotemperature, respectively). Previously reported records of seawater composition are primarily derived from fluid inclusions in marine evaporites; however, the results are sparse due to the limited availability of such deposits. In this thesis, changes in the Eocene seawater chemistry were reconstructed using trace element (elements/Ca) and isotopic (δ26Mg) proxies in a Larger Benthic Foraminifera (LBFs), i.e., Nummulites sp., to constrain the driving processes of long-term changes in seawater chemistry. To achieve the objective of this thesis, first, a measurement protocol was established using LA-ICPMS to measure the K/Ca ratio simultaneously with other element/calcium ratios, which is challenging due to the interference of ArH+ on K+. Utilising this newly established measurement protocol, laboratory-cultured Operculina ammonoides grown at different seawater calcium concentrations ([Ca2+]), repeated at different temperatures, as well as modern O. ammonoides collected from different regions exhibiting a range of seawater parameters, were investigated. A significant correlation was observed between K/Casw and K/CaLBF, allowing K/CaLBF to potentially be used as a proxy for seawater major ion reconstructions. In addition, modern O. ammonoides demonstrated no significant influence of most seawater parameters (temperature, salinity, pH, or [CO32-]) on K/CaLBF. Modern O. ammonoides were also assessed for their Mg isotopic composition (δ26Mg), revealing no significant effect of temperature or salinity on δ26MgLBF. Furthermore, the Mg isotopic fractionation in O. ammonoides was found to be close to that of inorganic calcite, indicating minimal vital effects in these large benthic foraminifera. Operculina ammonoides is the nearest living relative of the abundant Eocene genus Nummulites, enabling the reconstruction of seawater chemistry using the calibration based on O. ammonoides. The trace elemental/calcium proxies, including Na/Ca, K/Ca, and Mg/Ca, as well as the δ26Mg proxy, were investigated in Eocene Nummulites. The result showed that during the Eocene, [Ca2+]sw was 1.6-2 times higher, while [K+]sw was ~2 times lower than the modern seawater composition. Furthermore, [Mg2+]sw decreased from the early Eocene (54.3− +9 7..69 mmol kg-1 at ~55 Ma) to Late Eocene (37.8− +4 4..3 4 mmol kg-1 at ~31 Ma), followed by an increase toward modern seawater [Mg]. In contrast, the variability in δ26Mgsw values remained within a narrow range of ~0.3 ‰ throughout the Cenozoic. The reconstructed [Ca2+]sw agrees with the suggestion that Cenozoic seawater chemistry changes can be explained via a change in the seafloor spreading rate. When combined with existing records, the observed minimal change in δ26Mgsw with an increase in [Mg2+]sw suggests an additional possible role of a decrease in the formation of authigenic clay minerals coincident with the Cenozoic decline in deep ocean temperature, which is also supported by the increase in the [K+]sw reconstructed here for the first time. This finding highlights that the reduction in seafloor-spreading rate and decline in reverse weathering during the Cenozoic era has played a significant role in the evolution of seawater chemistry, emphasizing the importance of these processes in driving long-term changes in the carbon cycle.

show abstract

Section: Foraminifera: Marine Archives For Palaeoclimatic Reconstructionmentioning

confidence: 99%

Long-term variability of ocean chemistry : implications for deep-time palaeothermometry and the carbon cycle

Nambiar

View full text Add to dashboard Cite

show abstract

Foraminifers (Benthic)

Cited by 1 publication

References 29 publications

Long-term variability of ocean chemistry : implications for deep-time palaeothermometry and the carbon cycle

Long-term variability of ocean chemistry : implications for deep-time palaeothermometry and the carbon cycle

Contact Info

Product

Resources

About