Table_2_Impacts of glacial and sea-ice meltwater, primary production, and ocean CO2 uptake on ocean acidification state of waters by the 79 North Glacier and northeast Greenland shelf.pdf

The waters adjacent to the Nioghalvfjerdsbræ (79 North Glacier, 79NG) are influenced by Greenland Ice Sheet (GrIS) melt, sea-ice meltwater, and waters on the adjacent northeast Greenland shelf (NEGS). We investigated ocean acidification (OA) variables and the role of freshening, primary production, and air-sea CO2 exchange in Dijmphna Sound (DS) and on the NEGS in the summers of 2012 and 2016. The upper 150 m consisted of Polar Water with Arctic origin that was divided into a fresh surface layer (SL<50 m) and a cold halocline layer (CHL, 50 to 150 m). The layer below 150 m was of Atlantic origin. The SL freshwater was larger in 2012 than in 2016, mainly originated from local 79NG (and GrIS) runoff in DS, whereas on the NEGS in both years, it was mainly from sea-ice melt. The lowest aragonite saturation state (ΩAr) of 1.13 was found in the SL in 2012. Biological CO2 drawdown at primary production caused increased ΩAr in SL, which compensated for most of the ΩAr decrease due to the freshwater dilution of carbonate ions reducing total alkalinity, hence preventing corrosive conditions. This was most pronounced near the 79NG front in 2012, where surface stratification was most pronounced coinciding with large glacial meltwater fractions. Freshening decreased ΩAr by 0.4 at the 79NG front was compensated by biological CO2 drawdown by ~0.5. In 2016, a well-mixed water column in DS and NEGS, with dilution by sea-ice meltwater, caused less compensation on ΩAr by biological CO2 drawdown than in 2012. In future with changing climate and changing ocean chemistry, the increased meltwater effects may overcome the alleviating effects of biological CO2 drawdown on OA with unfavorable conditions for calcifying organisms. However, our study also suggests that primary production may be stimulated by stratification from surface meltwater. In addition, Atlantification and subglacial discharge may result in upwelling of inorganic nutrients that could promote primary production.

79北冰川（Nioghalvfjerdsbræ，79NG）毗邻海域受到格陵兰冰盖（Greenland Ice Sheet, GrIS）融水、海冰融水以及东北格陵兰陆架（Northeast Greenland Shelf, NEGS）周边水体的共同影响。本研究于2012年与2016年夏季，针对迪普姆纳湾（Dijmphna Sound, DS）及东北格陵兰陆架海域的海洋酸化（Ocean Acidification, OA）变量展开调查，同时分析了水体淡化、初级生产以及海-气CO₂交换在其中的作用。
研究区域内150米以浅水体为北极起源的极地水，可划分为淡水表层（Fresh Surface Layer, SL，水深<50m）与冷盐跃层（Cold Halocline Layer, CHL，水深50~150m）；150米以深水体则源自大西洋。2012年的表层淡水占比高于2016年：迪普姆纳湾的表层淡水主要来源于当地79北冰川（及格陵兰冰盖）的径流，而两年间东北格陵兰陆架的表层淡水均主要来自海冰融水。
2012年的淡水表层中测得最低文石饱和状态（aragonite saturation state, ΩAr）值为1.13。初级生产过程中的生物性CO₂消耗提升了表层水体的ΩAr，该过程抵消了因淡水稀释碳酸盐离子、降低总碱度所导致的大部分ΩAr下降，从而避免了水体出现腐蚀性环境。这一补偿效应在2012年79北冰川锋面附近最为显著：该区域表层水体层结最强，同时冰川融水占比极高。在79北冰川锋面处，水体淡化使ΩAr降低0.4，而生物性CO₂消耗抵消了约0.5的ΩAr降幅。
2016年，迪普姆纳湾与东北格陵兰陆架海域的水体混合充分，加之海冰融水的稀释作用，生物性CO₂消耗对ΩAr的补偿效应弱于2012年。在未来气候变化与海洋化学改变的背景下，融水影响的增强可能会抵消生物性CO₂消耗对海洋酸化的缓解作用，进而对钙化生物造成不利影响。不过本研究同时表明，表层融水形成的层结可能会促进初级生产。此外，大西洋化与冰下径流可能会带动无机营养盐上升，从而进一步推动初级生产活动。