Ross Ice Shelf Cavity Ocean Data

here we provide data from the ross ice shelf ocean cavity. location - the hwd2 camp was established in october of 2017 at 80o 39.497’s, 174o 27.678’e where the ice is moving seaward at around ~600 m a-1 and is sourced from the transantarctic mountains. profiling instruments - profiling was primarily conducted with an rbr concerto ctd (conductivity-temperature depth) profiling instrument, and this was cross-calibrated against irregular profiles with an rbr duet (pressure and temperature only), a sbe37 microcat ctd as well as moored sbe37 microcat ctds. the rbr unit is small and has suitable sensor capability (temperature and conductivity accuracies of ±0.002°c and ±0.003 ms cm-1). its conductivity cell design is not prone to fouling by ice crystals, making it ideal for work in the sometimes crystal-laden borehole conditions. we were inconsistent in how we mounted the ctd on its protective frame and this appeared to make small difference in the conductivity signal (resulting in an ~0.03 psu variation). this was post-corrected based on the essentially invariant mooring data from the lower water column as well as sbe37 cross-calibration profile data. because of the potential for sediment contamination of the sensors, the profiles were mostly conservative in their proximity to the sea floor. on several occasions, profiles were conducted all the way to the sea floor. the temperature and salinity are presented in eos-80 in order to compare with available data. eighty three profiles are provided here (ctd_hwd2_*.dat). in addition, limited microstructure profiling was conducted to provide insight into some of the mixing details.the profiles were conducted by lowering the instrument to the ice base then commencing a sequence of three up-down “yo-yos” before returning to the surface and downloading. a data segment is included here (vmp_hwd2.dat). there were some challenges registering the vertical coordinate for the profiles. the melting of the borehole generates a trapped pool of relatively fresh water. the interface between this and the ocean should be near the base of the hole or a little higher – with seawater intrusion. however, there were some instances where the interface was at a higher pressure (i.e. apparently in the open water column). the best explanation for this is that the water in the borehole is not at static equilibrium for some period after initial melting. we use 34.3 psu as a cut-off, in addition to a pressure criterion to identify the top of the useful oceanic profile. it is also not inconceivable that water was being ejected from the hole, but it is unlikely that this would have impacted in the consistent observed pattern. instrumented mooring - the mooring instruments at hwd2-a comprised 5 nortek aquadopp single point current meters in titanium housings reporting to the surface (30-minute interval, table si-three) via an inductive modem to a sound-9 data logger and iridium transmitter. the current meter measurements were corrected to account for the 138o magnetic declination offset (i.e. the south magnetic pole is to the north-west of the field site). five files are provided here (hwd2_init_rcm*.dat4). details in: stevens c, hulbe c, brewer m, stewart c, robinson n, ohneiser c and jendersie j, 2020. ocean mixing and heat transport processes observed under the ross ice shelf controls its basal melting, accepted pnas, may 2020.

本数据集提供了罗斯冰架海洋洞穴的数据。位置信息——2017年10月，在80°39.497'N，174°27.678'E处建立了HWD2营地，该处冰层以约600 m/a的速度向海移动，其水源来自南极横断山脉。测量仪器——主要使用RBR Concerto CTD（电导率-温度-深度）剖面测量仪器进行测量，并以此与RBR Duet（仅压力和温度）的不规则剖面、SBE37 Microcat CTD以及锚定SBE37 Microcat CTDs进行交叉校准。RBR设备体积小巧，具备适宜的传感器功能（温度和电导率精度为±0.002°C和±0.003 ms/cm-1）。其电导池设计不易受到冰晶的污染，因此适用于有时充满冰晶的钻孔条件。我们在将CTD安装在保护框架上的方式上存在不一致，这导致电导率信号出现细微差异（导致约0.03 psu的变化）。这一差异已根据底层水体基本恒定的锚定数据和SBE37交叉校准剖面数据进行后修正。由于传感器可能受到沉积物污染，剖面测量主要保守地靠近海底进行。在几次测量中，剖面测量一直进行到海底。温度和盐度以EOS-80表示，以便与现有数据进行比较。此处提供了八十三条剖面数据（ctd_hwd2_*.dat）。此外，还进行了有限的微结构剖面测量，以深入了解某些混合细节。剖面测量通过将仪器降至冰底，然后进行一系列的三次上浮-下沉“悠悠球”动作，返回水面并下载。此处包含一个数据段（vmp_hwd2.dat）。在注册剖面垂直坐标时遇到了一些挑战。钻孔的融化产生了一个相对新鲜的淡水被困池。该池与海洋之间的界面应接近孔底或略高——存在海水入侵。然而，在有些情况下，界面处于更高的压力（即似乎在开放的水柱中）。对此现象的最佳解释是，在初次融化后的一段时间内，钻孔中的水并未达到静态平衡。我们使用34.3 psu作为截止值，此外还使用压力标准来识别有用的海洋剖面顶部。也不排除水从孔中喷出的可能性，但这种情况不太可能影响观察到的持续模式。仪器锚定——HWD2-a的锚定仪器包括5个Nortek Aquadopp单点流速仪，这些流速仪在钛制外壳中报告给水面（30分钟间隔，表格SI-Three），通过感应调制解调器连接到Sound-9数据记录仪和铱发射器。流速仪测量值已校正以考虑138°的磁偏角偏差（即南磁极位于场地的西北方向）。此处提供了五个文件（hwd2_init_rcm*.dat4）。详细信息请参阅：Stevens C, Hulbe C, Brewer M, Stewart C, Robinson N, Ohneiser C 和 Jendersie J，2020.在南极罗斯冰架下观察到的海洋混合和热传输过程控制其底部融化，已接受PNAS，2020年5月。