Seasonal Changes in Dissolved Organic Matter Composition in a Patagonian Fjord Affected by Glacier Melt Inputs
Seasonal Changes in Dissolved Organic Matter Composition in a Patagonian Fjord Affected by Glacier Melt Inputs
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DOI：
10.3389/fmars.2021.612386
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发表时间：
2021-04
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影响因子：
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通讯作者：
M. Marshall;A. Kellerman;J. Wadham;J. Hawkings;G. Daneri;R. Torres;H. Pryer;A. Beaton;H. C. Ng;A. Urra;L. Robinson;R. Spencer
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作者：
M. Marshall;A. Kellerman;J. Wadham;J. Hawkings;G. Daneri;R. Torres;H. Pryer;A. Beaton;H. C. Ng;A. Urra;L. Robinson;R. Spencer
峡湾的生物地球化学过程可能受到周围冰川覆盖变化的影响，但对于融水如何直接影响峡湾的溶解有机质（DOM）知之甚少。此外，现有的数据仅限于北半球的几个地点。本文分析了智利巴塔哥尼亚（48°S） Baker-Martinez峡湾溶解有机碳（DOC）浓度和DOM组成的季节和空间变化（荧光光谱、超高分辨率质谱），以推断区域快速消冰对峡湾DOM的影响。我们发现，表层DOC浓度在季节之间没有显著变化，但DOM组成对河流输入的差异很敏感。在夏季，较高的蛋白样荧光反映了冰川融水输入的增加，而分子水平数据显示，由于分层更强烈，海洋DOM的影响较弱。我们假设河流和海水季节平衡的变化影响了表层生物活性肽的供应和有机氮的循环。DOM组成随盐度增加的趋势与河口的模式一致（即芳香化合物优先去除和不饱和和富含杂原子的海洋DOM的相对贡献增加）。初步估计还表明，这个峡湾每年至少10%的有机碳储量是由四条最大的冰川河流提供的，这些输入主要是溶解的（84%）颗粒有机碳。因此，河流DOC可能是峡湾内细菌群落的重要碳补贴。总的来说，研究结果强调了巴塔哥尼亚峡湾对冰川融化输入变化的生物地球化学敏感性，这可能与气候变暖的其他冰川峡湾有关。
Biogeochemical processes in fjords are likely affected by changes in surrounding glacier cover but very little is known about how meltwater directly influences dissolved organic matter (DOM) in fjords. Moreover, the data available are restricted to a handful of northern hemisphere sites. Here we analyze seasonal and spatial variation in dissolved organic carbon (DOC) concentration and DOM composition (spectrofluorescence, ultrahigh resolution mass spectrometry) in Baker-Martinez Fjord, Chilean Patagonia (48°S), to infer the impacts of rapid regional deglaciation on fjord DOM. We show that surface layer DOC concentrations do not vary significantly between seasons, but DOM composition is sensitive to differences in riverine inputs. In summer, higher protein-like fluorescence reflects increased glacial meltwater inputs, whilst molecular level data show weaker influence from marine DOM due to more intense stratification. We postulate that the shifting seasonal balance of riverine and marine waters affects the supply of biolabile peptides and organic nitrogen cycling in the surface layer. Trends in DOM composition with increasing salinity are consistent with patterns in estuaries (i.e. preferential removal of aromatic compounds and increasing relative contribution of unsaturated and heteroatom-rich DOM from marine sources). Preliminary estimates also suggest that at least 10% of the annual organic carbon stock in this fjord is supplied by the four largest, glacially fed rivers and that these inputs are dominated by dissolved (84%) over particulate organic carbon. Riverine DOC may therefore be an important carbon subsidy to bacterial communities in the inner fjord. The overall findings highlight the biogeochemical sensitivity of a Patagonian fjord to changes in glacier melt input, which likely has relevance for other glaciated fjords in a warming climate.