Ultraviolet radiation blocks the organic carbon exchange between the dissolved phase and the gel phase in the ocean
Ultraviolet radiation blocks the organic carbon exchange between the dissolved phase and the gel phase in the ocean
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DOI：
10.4319/lo.2003.48.4.1618
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发表时间：
2003-07-01
影响因子：
4.5
通讯作者：
Verdugo, P
中科院分区：
文献类型：
--
作者：
Orellana, MV;Verdugo, P
溶解有机碳（DOC）是地球上活性有机碳的主要储集层之一。虽然海洋DOC池的大部分主要由小的难降解聚合物材料组成，但新的证据表明，大约10%的DOC池（10(16)g C）可以通过形成微观凝胶进入微生物环，最终可以被细菌定植和降解。海洋微凝胶是由DOC聚合物自发可逆的组装/分散平衡形成水合钙键缠结聚合物网络而形成的。在这里，我们验证了紫外线（UV）光解理应该强烈抑制微凝胶形成的假设，因为缠结网络的稳定性随着聚合物长度呈指数级下降。由于臭氧屏蔽的丧失，太阳辐射的UV-B光谱成分（lambda = 280-320 nm）在过去几十年中急剧增加，特别是在极地地区。采用动态激光散射光谱和流式细胞术研究了紫外光在0.2 μ m过滤海水中诱导DOC聚合物的裂解，以及紫外光对DOC聚合/分散平衡的影响。结果表明，在夏至期间，海水暴露于相当于南极洲的UV-B通量，可以分裂DOC聚合物，抑制其自发组装，和/或分散组装的微凝胶。我们的结果与之前的观察结果一致，即紫外线光解产生的碎片随着暴露时间的增加呈指数增长，这表明紫外线可以通过阻碍微凝胶的形成来限制微生物底物的供应。紫外线裂解产生的短链聚合物不能组装，这可能最终解释了海水中发现的旧的难熔DOC池。
Dissolved organic carbon (DOC) is one of the major reservoirs of active organic carbon on Earth. Although the bulk of the marine DOC pool is largely composed of small refractory polymeric material, new evidence suggests that similar to10% of the DOC pool (10(16) g C) can enter the microbial loop by forming microscopic gels that can eventually be colonized and degraded by bacteria. Marine microgels result from a spontaneous and reversible assembly/dispersion equilibrium of DOC polymers forming hydrated Ca-bonded tangled polymer networks. Here we test the hypothesis that ultraviolet (UV) photocleavage should strongly inhibit the formation of microgels, because the stability of tangled networks decreases exponentially with polymer length. Because of the loss of ozone shielding, the UV-B spectral component of solar radiation (lambda = 280-320 nm) has undergone a dramatic increase in the past few decades, particularly in the polar regions. We used dynamic laser-scattering spectroscopy and flow cytometry to investigate UV-induced DOC polymer cracking and the effect of UV on DOC assembly/dispersion equilibrium in 0.2 mum filtered seawater. Results indicate that exposure of seawater to UV-B fluxes equivalent to those found in Antarctica during summer solstice can cleave DOC polymers, inhibit their spontaneous assembly, and/or disperse assembled microgels. Our results agree with previous observations that indicated that fragmentation produced by UV photolysis increases exponentially with exposure time and suggested that UV could limit the supply of microbial substrate by hindering microgel formation. UV cleavage yields short-chain polymers that do not assemble and could eventually account for the old refractory DOC pool found in seawater.