In:
Biogeosciences, Copernicus GmbH, Vol. 20, No. 9 ( 2023-05-09), p. 1725-1739
Abstract:
Abstract. Understanding the variations in past ocean carbonate chemistry is critical
to elucidating the role of the oceans in balancing the global carbon cycle.
The fossil shells from marine calcifiers present in the sedimentary record
are widely applied as past ocean carbon cycle proxies. However, the
interpretation of these records can be challenging due to the complex
physiological and ecological response to the carbonate system during an
organisms' life cycle and the potential for preservation at the
seafloor. Here we present a new dissolution proxy based on the morphological
attributes of coccolithophores from the Noëlaerhabdaceae family
(Emiliania huxleyi 〉 2 µm, and small Gephyrocapsa spp.). To evaluate the influences of
coccolithophore calcification and coccolith preservation on fossil
morphology, we measured morphological attributes, mass, length, thickness,
and shape factor (ks) of coccoliths in a laboratory dissolution experiment
and surface sediment samples from the South China Sea. The coccolith
morphological data in surface sediments were also analyzed with environment
settings, namely surface temperature, nutrients, pH, chlorophyll a
concentration, and carbonate saturation of bottom water by a redundancy
analysis. Statistical analysis indicates that carbonate saturation of the
deep ocean explains the highest proportion of variation in the morphological
data instead of the environmental variables of the surface ocean. Moreover,
the dissolution trajectory in the ks vs. length of coccoliths is comparable
between natural samples and laboratory dissolution experiments, emphasizing
the importance of carbonate saturation on fossil coccolith morphology.
However, the mean ks alone cannot fully explain the main variations observed
in our work. We propose that the normalized ks variation (σ/ks), which is the ratio between the standard deviation of ks (σ) and the mean
ks,
could reflect different degrees of dissolution and size-selective
dissolution, influenced by the assemblage composition. Applied together
with the σ/ks ratio, the ks factor of fossil coccoliths in deep
ocean sediments could be a potential proxy for a quantitative reconstruction
of past carbonate dissolution dynamics.
Type of Medium:
Online Resource
ISSN:
1726-4189
DOI:
10.5194/bg-20-1725-2023
Language:
English
Publisher:
Copernicus GmbH
Publication Date:
2023
detail.hit.zdb_id:
2158181-2
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