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Spring thaw ionic pulses boost nutrient availability and microbial growth in entombed Antarctic Dry Valley cryoconite holes.

Telling J, Anesio AM, Tranter M, Fountain AG, Nylen T, Hawkings J, Singh VB, Kaur P, Musilova M, Wadham JL - Front Microbiol (2014)

Bottom Line: Rates of bacterial production were significantly elevated during the ionic pulse, likely due to the increased nutrient availability.There was no concomitant increase in photosynthesis rates, with a net depletion of dissolved inorganic carbon suggesting inorganic carbon limitation.Potential nitrogen fixation was detected in fully melted holes where it could be an important source of nitrogen to support microbial growth, but not during the ionic pulse where nitrogen availability was higher.

View Article: PubMed Central - PubMed

Affiliation: School of Geographical Sciences, University of Bristol Bristol, UK.

ABSTRACT
The seasonal melting of ice entombed cryoconite holes on McMurdo Dry Valley glaciers provides oases for life in the harsh environmental conditions of the polar desert where surface air temperatures only occasionally exceed 0°C during the Austral summer. Here we follow temporal changes in cryoconite hole biogeochemistry on Canada Glacier from fully frozen conditions through the initial stages of spring thaw toward fully melted holes. The cryoconite holes had a mean isolation age from the glacial drainage system of 3.4 years, with an increasing mass of aqueous nutrients (dissolved organic carbon, total nitrogen, total phosphorus) with longer isolation age. During the initial melt there was a mean nine times enrichment in dissolved chloride relative to mean concentrations of the initial frozen holes indicative of an ionic pulse, with similar mean nine times enrichments in nitrite, ammonium, and dissolved organic matter. Nitrate was enriched twelve times and dissolved organic nitrogen six times, suggesting net nitrification, while lower enrichments for dissolved organic phosphorus and phosphate were consistent with net microbial phosphorus uptake. Rates of bacterial production were significantly elevated during the ionic pulse, likely due to the increased nutrient availability. There was no concomitant increase in photosynthesis rates, with a net depletion of dissolved inorganic carbon suggesting inorganic carbon limitation. Potential nitrogen fixation was detected in fully melted holes where it could be an important source of nitrogen to support microbial growth, but not during the ionic pulse where nitrogen availability was higher. This study demonstrates that ionic pulses significantly alter the timing and magnitude of microbial activity within entombed cryoconite holes, and adds credence to hypotheses that ionic enrichments during freeze-thaw can elevate rates of microbial growth and activity in other icy habitats, such as ice veins and subglacial regelation zones.

No MeSH data available.


Related in: MedlinePlus

Enrichment factors (XF) for aqueous ions and cryoconite bacterial production and photosynthesis vs. δ18O-H20 (a measure of the % ice melt). Enrichment factors are the ratio of the measured aqueous concentrations of the ion to the mean concentration of that ion in initial frozen cryoconite holes. Statistics refer to Pearson correlation coefficients after taking the logarithm of the enrichment factor.
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Figure 1: Enrichment factors (XF) for aqueous ions and cryoconite bacterial production and photosynthesis vs. δ18O-H20 (a measure of the % ice melt). Enrichment factors are the ratio of the measured aqueous concentrations of the ion to the mean concentration of that ion in initial frozen cryoconite holes. Statistics refer to Pearson correlation coefficients after taking the logarithm of the enrichment factor.

Mentions: Ice core and aqueous geochemistry of cryoconite holes is summarized in Table 2. Mean chloride concentrations in fully frozen cryoconite holes were enriched 3.2× over ice cores (Table 3, Figure 1). Mean enrichment factors for Ca2+ (20.7×), Mg2+ (8.2×), and SO2−4 (9.1×) were higher than those of Cl− (Table 3, Figure 1). Mean enrichment factors for DIC (3.1×) were similar to those of Cl−, DOC (2.4×), Na+ (2.0×), and K+ (2.6×). All dissolved nitrogen and phosphorus species (NO−3, NH+4, NO−2, DON, DOP, PO3−4) were depleted relative to Cl− with enrichment factors <2× (Table 3, Figure 1).


Spring thaw ionic pulses boost nutrient availability and microbial growth in entombed Antarctic Dry Valley cryoconite holes.

Telling J, Anesio AM, Tranter M, Fountain AG, Nylen T, Hawkings J, Singh VB, Kaur P, Musilova M, Wadham JL - Front Microbiol (2014)

Enrichment factors (XF) for aqueous ions and cryoconite bacterial production and photosynthesis vs. δ18O-H20 (a measure of the % ice melt). Enrichment factors are the ratio of the measured aqueous concentrations of the ion to the mean concentration of that ion in initial frozen cryoconite holes. Statistics refer to Pearson correlation coefficients after taking the logarithm of the enrichment factor.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4263180&req=5

Figure 1: Enrichment factors (XF) for aqueous ions and cryoconite bacterial production and photosynthesis vs. δ18O-H20 (a measure of the % ice melt). Enrichment factors are the ratio of the measured aqueous concentrations of the ion to the mean concentration of that ion in initial frozen cryoconite holes. Statistics refer to Pearson correlation coefficients after taking the logarithm of the enrichment factor.
Mentions: Ice core and aqueous geochemistry of cryoconite holes is summarized in Table 2. Mean chloride concentrations in fully frozen cryoconite holes were enriched 3.2× over ice cores (Table 3, Figure 1). Mean enrichment factors for Ca2+ (20.7×), Mg2+ (8.2×), and SO2−4 (9.1×) were higher than those of Cl− (Table 3, Figure 1). Mean enrichment factors for DIC (3.1×) were similar to those of Cl−, DOC (2.4×), Na+ (2.0×), and K+ (2.6×). All dissolved nitrogen and phosphorus species (NO−3, NH+4, NO−2, DON, DOP, PO3−4) were depleted relative to Cl− with enrichment factors <2× (Table 3, Figure 1).

Bottom Line: Rates of bacterial production were significantly elevated during the ionic pulse, likely due to the increased nutrient availability.There was no concomitant increase in photosynthesis rates, with a net depletion of dissolved inorganic carbon suggesting inorganic carbon limitation.Potential nitrogen fixation was detected in fully melted holes where it could be an important source of nitrogen to support microbial growth, but not during the ionic pulse where nitrogen availability was higher.

View Article: PubMed Central - PubMed

Affiliation: School of Geographical Sciences, University of Bristol Bristol, UK.

ABSTRACT
The seasonal melting of ice entombed cryoconite holes on McMurdo Dry Valley glaciers provides oases for life in the harsh environmental conditions of the polar desert where surface air temperatures only occasionally exceed 0°C during the Austral summer. Here we follow temporal changes in cryoconite hole biogeochemistry on Canada Glacier from fully frozen conditions through the initial stages of spring thaw toward fully melted holes. The cryoconite holes had a mean isolation age from the glacial drainage system of 3.4 years, with an increasing mass of aqueous nutrients (dissolved organic carbon, total nitrogen, total phosphorus) with longer isolation age. During the initial melt there was a mean nine times enrichment in dissolved chloride relative to mean concentrations of the initial frozen holes indicative of an ionic pulse, with similar mean nine times enrichments in nitrite, ammonium, and dissolved organic matter. Nitrate was enriched twelve times and dissolved organic nitrogen six times, suggesting net nitrification, while lower enrichments for dissolved organic phosphorus and phosphate were consistent with net microbial phosphorus uptake. Rates of bacterial production were significantly elevated during the ionic pulse, likely due to the increased nutrient availability. There was no concomitant increase in photosynthesis rates, with a net depletion of dissolved inorganic carbon suggesting inorganic carbon limitation. Potential nitrogen fixation was detected in fully melted holes where it could be an important source of nitrogen to support microbial growth, but not during the ionic pulse where nitrogen availability was higher. This study demonstrates that ionic pulses significantly alter the timing and magnitude of microbial activity within entombed cryoconite holes, and adds credence to hypotheses that ionic enrichments during freeze-thaw can elevate rates of microbial growth and activity in other icy habitats, such as ice veins and subglacial regelation zones.

No MeSH data available.


Related in: MedlinePlus