The pH dependency of the boron isotopic composition of diatom opal (<i>Thalassiosira weissflogii</i>)
<p>The high-latitude oceans are key areas of carbon and heat exchange between the atmosphere and the ocean. As such, they are a focus of both modern oceanographic and palaeoclimate research. However, most palaeoclimate proxies that could provide a long-term perspective are based on calcareous...
| Main Authors: | , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2020-05-01
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| Series: | Biogeosciences |
| Online Access: | https://www.biogeosciences.net/17/2825/2020/bg-17-2825-2020.pdf |
| Summary: | <p>The high-latitude oceans are key areas of carbon and heat exchange between
the atmosphere and the ocean. As such, they are a focus of both modern
oceanographic and palaeoclimate research. However, most palaeoclimate
proxies that could provide a long-term perspective are based on calcareous
organisms, such as foraminifera, that are scarce or entirely absent in
deep-sea sediments south of 50<span class="inline-formula"><sup>∘</sup></span> S in the Southern Ocean and north
of 40<span class="inline-formula"><sup>∘</sup></span> N in the North Pacific. As a result, proxies need to be
developed for the opal-based organisms (e.g. diatoms) found at these high
latitudes, which dominate the biogenic sediments recovered from these
regions. Here we present a method for the analysis of the boron (B) content
and isotopic composition (<span class="inline-formula"><i>δ</i><sup>11</sup></span>B) of diatom opal. We apply it for
the first time to evaluate the relationship between seawater pH, <span class="inline-formula"><i>δ</i><sup>11</sup></span>B and B concentration ([B]) in the frustules of the diatom
<i>Thalassiosira weissflogii</i>, cultured across a range of carbon dioxide partial pressure (<span class="inline-formula"><i>p</i>CO<sub>2</sub></span>) and
pH values. In agreement with existing data, we find that the [B]
of the cultured diatom frustules increases with increasing pH (Mejía et al.,
2013). <span class="inline-formula"><i>δ</i><sup>11</sup></span>B shows a relatively well defined negative trend with
increasing pH, completely distinct from any other biomineral previously
measured. This relationship not only has implications for the magnitude of
the isotopic fractionation that occurs during boron incorporation into opal,
but also allows us to explore the potential of the boron-based proxies for
palaeo-pH and palaeo-<span class="inline-formula">CO<sub>2</sub></span> reconstruction in high-latitude marine
sediments that have, up until now, eluded study due to the lack of suitable
carbonate material.</p> |
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| ISSN: | 1726-4170 1726-4189 |