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| Titel |
Multi-centennial Record of Labrador Sea Primary Productivity and Sea-Ice Variability Archived in Coralline Algal Ba/Ca |
| VerfasserIn |
Phoebe Chan, Jochen Halfar, Walter Adey, Steffen Hetzinger, Thomas Zack, Kent Moore, Ulrich Wortmann, Branwen Williams, Alicia Hou |
| Konferenz |
EGU General Assembly 2017
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 19 (2017) |
| Datensatznummer |
250138544
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| Publikation (Nr.) |
 EGU/EGU2017-1592.pdf |
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| Zusammenfassung |
| Arctic sea-ice thickness and concentration have dropped by approximately 9% per decade
since 1978. Concurrent with this sea-ice decline is an increase in rates of phytoplankton
productivity, driven by shoaling of the mixed layer and enhanced transmittance of solar
radiation into the surface ocean. This has recently been confirmed by phytoplankton studies
in Arctic and Subarctic basins that have revealed earlier timing, prolonged duration, and
increased primary productivity of the spring phytoplankton bloom. However, difficulties of
navigating in remote ice-laden waters and harsh polar climates have often resulted in short
and incomplete records of in-situ plankton abundance in the northwestern Labrador Sea.
Alternatively, information of past ocean productivity may be gained through the study of
trace nutrient distributions in the surface water column. Investigations of dissolved barium
(Ba) concentrations in the Arctic reveal significant depletions of Ba in surface seawaters due
to biological scavenging during the spring phytoplankton bloom. Here we apply
a barium-to-calcium (Ba/Ca) and carbon isotope (δ13C) multiproxy approach to
long-lived crustose coralline algae in order to reconstruct an annually-resolved
multi-centennial record of Labrador Sea productivity related to sea-ice variability in
Labrador, Canada that extends well into the Little Ice Age (LIA; 1646 AD). The
crustose coralline alga Clathromorphum compactum is a shallow marine calcareous
plant that is abundant along the eastern Canadian coastline, and produces annual
growth increments which allow for the precise calendar dating and geochemical
sampling of hard tissue. Algal Ba/Ca ratios can serve as a promising new proxy for
surface water productivity, demonstrating a close correspondence to δ13C that does
not suffer from the anthropogenically-induced carbon isotope decline (ex. Suess
Effect) beginning in the 1960s. Coralline algal Ba/Ca demonstrates statistically
significant correlations to both observational and proxy records of sea-ice extent and
transport variability, and shows a persistent pattern of covariability that is broadly
consistent with the timing and phasing of the Atlantic Multidecadal Oscillation
(AMO). Lower algal Ba/Ca values are interpreted as increased productivity (via
biological scavenging) coinciding with warming sea surface temperatures and melting of
sea-ice, and vice versa. This relationship is further supported by negative correlations
between algal Ba/Ca and spatially averaged chlorophyll α concentrations determined
from Sea-Viewing Wide Field-of-View Sensor (SeaWiFS; 1998 – 2009) ocean
colour data. Extended comparisons to a multi-centennial tree-ring proxy AMO index
demonstrates more frequent positive Ba/Ca excursions (indicating reduced productivity)
associated with AMO cool phases during the Little Ice Age, followed by a step-wise
decline in Ba/Ca (indicating increasing productivity) from 1910 to present levels –
unprecedented in the last 365 years. Our multi-centennial record of coralline algal Ba/Ca in
the Subarctic northwest Atlantic demonstrates a long-term increasing trend in primary
productivity that is in agreement with recent satellite-based productivity in the
Arctic Ocean. This ongoing increase in phytoplankton productivity is expected
to fundamentally alter marine biodiversity and trophic dynamics as warming and
freshening of the surface layer is projected to intensify over the coming century. |
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