Dissolved organic nutrients dominate melting surface ice of the Dark Zone (Greenland Ice Sheet)
<p>Glaciers and ice sheets host abundant and dynamic communities of microorganisms on the ice surface (supraglacial environments). Recently, it has been shown that Streptophyte glacier algae blooming on the surface ice of the south-western coast of the Greenland Ice Sheet are a significant con...
Main Authors: | , , , , , , , , , , |
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Format: | Article |
Language: | English |
Published: |
Copernicus Publications
2019-08-01
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Series: | Biogeosciences |
Online Access: | https://www.biogeosciences.net/16/3283/2019/bg-16-3283-2019.pdf |
Summary: | <p>Glaciers and ice sheets host abundant and dynamic communities of
microorganisms on the ice surface (supraglacial environments). Recently, it
has been shown that Streptophyte glacier algae blooming on the surface ice
of the south-western coast of the Greenland Ice Sheet are a significant
contributor to the 15-year marked decrease in albedo. Currently, little is
known about the constraints, such as nutrient availability, on this
large-scale algal bloom. In this study, we investigate the relative
abundances of dissolved inorganic and dissolved organic macronutrients (N
and P) in these darkening surface ice environments. Three distinct ice
surfaces, with low, medium and high visible impurity loadings, supraglacial
stream water and cryoconite hole water, were sampled. Our results show a
clear dominance of the organic phase in all ice surface samples containing
low, medium and high visible impurity loadings, with 93 % of the total
dissolved nitrogen and 67 % of the total dissolved phosphorus in the
organic phase. Mean concentrations in low, medium and high visible impurity
surface ice environments are 0.91, 0.62 and 1.0 <span class="inline-formula">µ</span>M for dissolved inorganic nitrogen (DIN), 5.1, 11 and 14 <span class="inline-formula">µ</span>M for dissolved organic nitrogen (DON), 0.03, 0.07 and 0.05 <span class="inline-formula">µ</span>M for dissolved inorganic phosphorus (DIP) and 0.10, 0.15 and 0.12 <span class="inline-formula">µ</span>M for dissolved organic phosphorus
(DOP), respectively. DON concentrations in all three surface ice samples are
significantly higher than DON concentrations in supraglacial streams and
cryoconite hole water (0 and 0.7 <span class="inline-formula">µ</span>M, respectively). DOP
concentrations are higher in all three surface ice samples compared to
supraglacial streams and cryoconite hole water (0.07 <span class="inline-formula">µ</span>M for both).
Dissolved organic carbon (DOC) concentrations increase with the amount of
visible impurities present (low: 83 <span class="inline-formula">µ</span>M, medium: 173 <span class="inline-formula">µ</span>M and
high: 242 <span class="inline-formula">µ</span>M) and are elevated compared to supraglacial streams and
cryoconite hole water (30 and 50 <span class="inline-formula">µ</span>M, respectively). We
speculate that the architecture of the weathering crust, which impacts on
water flow paths and storage in the melting surface ice and/or the
production of extracellular polymeric substances (EPS), containing both N
and P in conjunction with C, is responsible for the temporary retention of
DON and DOP in the melting surface ice. The unusual presence of measurable DIP
and DIN, principally as <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M11" display="inline" overflow="scroll" dspmath="mathml"><mrow class="chem"><msubsup><mi mathvariant="normal">NH</mi><mn mathvariant="normal">4</mn><mo>+</mo></msubsup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="24pt" height="15pt" class="svg-formula" dspmath="mathimg" md5hash="8cff18dc7544e09830abea500d71300b"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="bg-16-3283-2019-ie00001.svg" width="24pt" height="15pt" src="bg-16-3283-2019-ie00001.png"/></svg:svg></span></span>, in the melting surface ice
environments suggests that factors other than macronutrient limitation are
controlling the extent and magnitude of the glacier algae.</p> |
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ISSN: | 1726-4170 1726-4189 |