Whitings, a sedimentologic dilemma
Whitings, a sedimentologic dilemma
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鳕鱼，沉积学困境
DOI：
10.1306/212f8f3a-2b24-11d7-8648000102c1865d
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发表时间：
1989
影响因子：
2
通讯作者：
P. Swart
中科院分区：
文献类型：
--
作者：
E. Shinn;R. Steinen;B. Lidz;P. Swart
鳕鱼是一种漂浮的水云，由于悬浮的碳酸盐而呈乳白色，据称源自底栖鱼类的作用或碳酸钙的直接沉淀。不同季节的五次航行前往大巴哈马浅滩，收集与争议相关的数据。测量的颗粒浓度平均为 10 毫克/升，其中悬浮在鳕鱼水中的碳酸盐沉积物最多为 20 毫克/升，而鳕鱼之外的清水的平均浓度为 1.5 毫克/升。这些颗粒主要是针状文石，但某些鳕鱼中的镁方解石含量高达 20%。使用固定沉积物收集器和流动沉积物收集器测量的沉积速率高达34 g/m 2 /hr。悬浮在鳕鱼中的沉积物聚集成淤泥和沙子大小的絮状物，并在六小时内沉降到沉淀池的底部，即使在摇晃的船上也是如此。人工鳕鱼中的沉积物是通过用虾拖网搅拌底部的沉积物而产生的，大约在同一时间沉降到底部。另一方面，从未观察到天然鳕鱼消散。由于鳕鱼的沉积速度足以导致鳕鱼在六小时内消散，因此我们得出结论，天然鳕鱼会通过直接降水不断得到补充。在鳕鱼中寻找鱼类利用了侧扫声纳和测深仪成像、虾拖网、鱼藤酮、远程视频和直接水肺观察。这些方法和 25 年的随意观察表明，鱼类并未参与大多数巴哈马鳕鱼的形成。在岩石或沙质底部发现了一些鳕鱼，那里没有可供鱼悬浮的泥浆。这些鳕鱼距泥泞底部区域的距离使得它们不可能被鱼类带到其他地方。稳定的碳和氧同位素分析和 Delta 14 C 活性被解释为表明鳕鱼中的悬浮沉积物含有一些沉淀碳酸钙，而不仅仅是搅拌成悬浮液的底部沉积物。据估计，大巴哈马浅滩鳕鱼中产生的新碳酸盐数量大大高于藻类生产产生的碳酸盐数量。因此，输送到深水中的沉积物量可能比之前想象的要多得多。
Whitings, drifting clouds of water, milky because of suspended carbonate, have been claimed to originate from either the action of bottom-feeding fish or direct precipitation of calcium carbonate. Five cruises during different seasons were made to the Great Bahama Bank to collect data pertinent to the controversy. Measurements of particulate concentrations average 10 mg/liter with a maximum of 20 mg/liter of carbonate sediment suspended in whiting water, compared with an average of 1.5 mg/liter for clear water outside the whitings. The particles are dominantly acicular aragonite, but Mg calcite composes as much as 20 percent of some whitings. Sedimentation rates, measured with fixed and drifting sediment traps, were as great as 34 g/m 2 /hr. Sediment suspended in whitings aggregated into silt- and sand-size fioccules and settled to the bottom of settling tanks within six hours, even on a rocking ship. Sediment in artificial whitings, created by stirring sediment from the bottom with a shrimp trawl, settled to the bottom in about the same time. Natural whitings, on the other hand, were never observed to dissipate. Because sedimentation from whitings occurs at rates sufficient to cause dissipation of the whitings within six hours, we conclude that the natural whitings are continually replenished by direct precipitation. The search for fish in whitings utilized sidescan sonar and fathometer imaging, shrimp trawls, rotenone, remote video, and direct scuba observation. These methods and 25 years of casual observations leading to this study indicate that fish are not involved in the formation of most Bahamian whitings. Several whitings were found over rocky or sandy bottoms where there was no mud available for fish to suspend. The distance of these whitings from areas of muddy bottom precluded their having been made elsewhere by fish. Stable carbon- and oxygen-isotopic analyses and Delta 14 C activity are interpreted to indicate that the suspended sediment in whitings contains some precipitated calcium carbonate and is not merely bottom sediment stirred into suspension. Estimates indicate that the amount of new carbonate produced in whitings on the Great Bahama Bank is substantially higher than that arising from algal production. Consequently, the amount of sediment transported to deep water may be much greater than previously thought.