Circulation and dispersal in California’s Borderland Basins

IF 3.8 3区 地球科学 Q1 OCEANOGRAPHY
James C. McWilliams , Pierre Damien , Faycal Kessouri
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引用次数: 0

Abstract

The Borderland Basins off Southern California are semi-isolated sea-floor depressions with connections to each other and to the open Pacific Ocean over narrow sills. A high-resolution, multi-year simulation is analyzed for its currents, stratification, and dissolved oxygen, with a focus on the mean conditions, intrinsic variability, and exchange rates with surrounding waters. The three shallowest, closest basins are given the most attention: Santa Barbara, Santa Monica, and San Pedro. Below the basin sill depths, the water masses in the basins are distinct from surrounding waters at the same density indicating a degree of dynamical isolation. The mean circulations are anti-clockwise around the topographic edges of the basins, consistent with eddy-driven flows (i.e., topostrophy). The mesoscale eddy variability is stronger than the mean flow, and at least partially it is comprised of topographic Rossby waves circuiting the edge slopes. Its magnitude is similar to the high-frequency currents (mostly tidal). There are recurrent cross-sill flows driven by an unbalanced pressure-gradient force, and these intermittently cause water mass flushing of the basins. The oxygen levels in the basins are occasionally anoxic, and they are maintained by a balance of downward physical transport from above, local respiration, and flux into the sediments. From a combination of multiple means of estimation, the deep basin water mass renewal times are on the order of a year or more, and this time is somewhat shorter in the Santa Barbara Basin than the others. The renewal processes are by intermittent sill overflows and by vertical exchanges through eddies and tides.

加利福尼亚边疆盆地的循环与扩散
南加州外海的边疆盆地是半孤立的海底洼地,通过狭窄的岩缝相互连接,并与开阔的太平洋相连。对其海流、分层和溶解氧进行了高分辨率的多年模拟分析,重点是平均状况、内在变化以及与周围水域的交换率。三个最浅、距离最近的盆地最受关注:圣巴巴拉、圣莫尼卡和圣佩德罗。在盆地边缘深度以下,盆地中的水团在密度相同的情况下与周围水域截然不同,这表明了一定程度的动态隔离。盆地地形边缘的平均环流为逆时针方向,与涡流驱动的水流(即地形营养)相一致。中尺度涡旋变化强于平均环流,至少部分是由环绕边缘斜坡的地形罗斯比波构成的。其幅度与高频海流(主要是潮汐)相似。在不平衡压力梯度力的驱动下,经常出现横溢流,这些横溢流间歇性地对盆地造成水团冲刷。盆地中的氧含量偶尔会缺氧,并通过从上方向下的物理输送、当地的呼吸作用和进入沉积物的通量之间的平衡来维持。综合多种估算方法,盆地深层水体的更新时间约为一年或更长,圣巴巴拉盆地的更新时间略短于其他盆地。更新过程是通过间歇性的溢流以及漩涡和潮汐进行垂直交换。
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来源期刊
Progress in Oceanography
Progress in Oceanography 地学-海洋学
CiteScore
7.20
自引率
4.90%
发文量
138
审稿时长
3 months
期刊介绍: Progress in Oceanography publishes the longer, more comprehensive papers that most oceanographers feel are necessary, on occasion, to do justice to their work. Contributions are generally either a review of an aspect of oceanography or a treatise on an expanding oceanographic subject. The articles cover the entire spectrum of disciplines within the science of oceanography. Occasionally volumes are devoted to collections of papers and conference proceedings of exceptional interest. Essential reading for all oceanographers.
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