(Table 1) Characteristics of marine snow and ice samples at Barrow, Alaska

We measured light absorption in 42 marine snow, sea ice, seawater, brine, and frost flower samples collected during the OASIS field campaign between February 27 and April 15, 2009. Samples represented multiple sites between landfast ice and open pack ice in coastal areas approximately 5 km west of Barrow, Alaska. The chromophores that are most commonly measured in snow, H2O2, NO3-, and NO2-, on average account for less than 1% of sunlight absorption in our samples. Instead, light absorption is dominated by unidentified "residual" species, likely organic compounds. Light absorption coefficients for the frost flowers on first-year sea ice are, on average, 40 times larger than values for terrestrial snow samples at Barrow, suggesting very large rates of photochemical reactions in frost flowers. For our marine samples the calculated rates of sunlight absorption and OH production from known chromophores are (0.1-1.4) x 10**14 (photons/cm**3/s) and (5-70) x 10**-12 (mol/L/s), respectively. Our residual spectra are similar to spectra of marine chromophoric dissolved organic matter (CDOM), suggesting that CDOM is the dominant chromophore in our samples. Based on our light absorption measurements we estimate dissolved organic carbon (DOC) concentrations in Barrow seawater and frost flowers as approximately 130 and 360 µM C, respectively. We expect that CDOM is a major source of OH in our marine samples, and it is likely to have other significant photochemistry as well.

本研究于2009年2月27日至4月15日开展的OASIS野外考察期间，采集了42份海洋雪、海冰、海水、卤水及霜花样本，并对其光吸收特性进行了测定。采样点位于阿拉斯加巴罗（Barrow）以西约5公里的沿岸区域，覆盖固定冰与开阔浮冰群之间的多个位点。雪中常见的测量发色团（chromophore）——过氧化氢（H₂O₂）、硝酸根（NO₃⁻）与亚硝酸根（NO₂⁻），在本研究样本中平均仅贡献不足1%的太阳光吸收。取而代之的是，太阳光吸收主要由未被识别的“残留”组分主导，此类组分大概率为有机化合物。一年生海冰上的霜花的光吸收系数，平均而言是巴罗地区陆地雪样的40倍，表明霜花内的光化学反应速率极高。针对本研究中的海洋样本，由已知发色团计算得到的太阳光吸收速率与羟基自由基（OH）生成速率分别为(0.1~1.4)×10¹⁴ 光子/(cm³·s)与(5~70)×10⁻¹² mol/(L·s)。本研究的残留光谱与海洋有色溶解有机物（chromophoric dissolved organic matter, CDOM）的光谱特征高度相似，表明CDOM是本研究样本中的主要发色团。基于本次光吸收测量结果，我们估算得到巴罗海域海水与霜花中的溶解有机碳（dissolved organic carbon, DOC）浓度分别约为130 μM C与360 μM C。我们推测CDOM是本研究海洋样本中羟基自由基的主要来源，且其大概率还参与其他重要的光化学反应过程。