Antarctic Circumpolar Current transport through Drake Passage: What can we learn from comparing high-resolution model results to observations?

Datasets for the Journal of Geophysical Research: Oceans publication: "Antarctic Circumpolar Current transport through Drake Passage: What can we learn from comparing high-resolution model results to observations?" [Abstract] Uncertainty exists in the time-mean total transport of the Antarctic Circumpolar Current (ACC), the world’s strongest ocean current. The two most recent observational programs in Drake Passage, DRAKE and cDrake, yielded transports of 141 and 173.3 Sv, respectively. In this paper, we use a realistic 1/12° global ocean simulation to interpret these observational estimates and reconcile their differences. We first show that the modeled ACC transport in the upper 1000 m is in excellent agreement with repeat shipboard acoustic Doppler current profiler (SADCP) transects and that the exponentially decaying transport profile in the model is consistent with the profile derived from repeat hydrographic data. By further comparing the model results to the cDrake and DRAKE observations, we argue that the modeled 157.3 Sv transport, i.e. approximately the average of the cDrake and DRAKE estimates, is actually representative of the time-mean ACC transport through the Drake Passage. The cDrake experiment overestimates the barotropic contribution in part because the array undersampled the deep recirculation southwest of the Shackleton Fracture Zone, whereas the surface geostrophic currents used in the DRAKE estimate yielded a weaker near-surface transport than implied by the SADCP data. We also find that the modeled baroclinic and barotropic transports are not correlated, thus monitoring either baroclinic or barotropic transport alone may be insufficient to assess the temporal variability of the total ACC transport.本数据集服务于《地球物理研究杂志：海洋》（Journal of Geophysical Research: Oceans）刊载的论文《德雷克海峡南极绕极流输运：对比高分辨率模式结果与观测资料可获得哪些启示》[摘要]。南极绕极流（Antarctic Circumpolar Current, ACC）作为全球强度最高的海洋流系，其时间平均总输运量仍存在不确定性。德雷克海峡近年开展的两项最新观测计划DRAKE与cDrake，分别得到141斯维德里（Sverdrup, Sv）与173.3斯维德里的输运量估算结果。本文采用1/12°分辨率的真实全球海洋数值模拟试验，对上述两项观测估算结果展开解读并调和二者的分歧。我们首先证实，模式模拟的1000米以浅南极绕极流输运量，与重复船载声学多普勒海流剖面仪（shipboard acoustic Doppler current profiler, SADCP）断面观测结果吻合极佳；且模式中呈指数衰减的输运剖面，与重复水文观测资料推导得到的剖面相一致。通过进一步将模式结果与cDrake、DRAKE观测资料开展对比，我们认为模式模拟得到的157.3 Sv输运量——即cDrake与DRAKE两项估算结果的平均值——实际上可代表德雷克海峡南极绕极流的时间平均总输运量。cDrake试验高估了正压（barotropic）输运分量，部分原因在于该观测阵列对沙克尔顿断裂带西南侧的深层回流采样不足；而DRAKE估算中所使用的海面地转流，得到的近表层输运量较SADCP资料的推断结果偏弱。我们还发现，模式模拟的斜压（baroclinic）输运与正压输运之间不存在相关性，因此仅监测斜压或正压输运中的任意一项，或不足以评估南极绕极流总输运量的时间变异性。