Box Coring – One Muddy Playground for Scientists
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By Anastasia Zhuravleva
Is it surprising that our modern society is highly affected by climatic instabilities and rapid environmental shifts? Apparently, not! Meanwhile, dramatic changes have been observed in the Arctic during the past few thousand years, which are expressed as temperature increase and sea ice decline. Within the marine environment, these variabilities are documented in the uppermost sediment layer. However, “the precious mud” deposited within the upper centimetres is often disturbed by coring. Therefore, recent climatic signals are either heavily hampered or just not preserved in records at all. Identification of historically-documented climatic fluctuations (e.g. the Roman Warm Period, the Dark Ages Cold Period, the Medieval Climate Anomaly, the Little Ice Age and the Modern (Industrial) Period), unfortunately, is vague or simply not possible. This problem becomes particularly important in the Arctic, where the sedimentation rates are relatively low during warm geological periods.
To provide dependable data from the upper sediment, in addition to main coring strategies (gravity cores and kastenlot cores) we use (giant) box cores, which, apparently, are well known for recovery of short and undisturbed marine archives. The basic principle behind box coring is cutting off a cubic block of sediment from the sea floor. Depending on the sediment properties, a box core retrieves on average a block of 40-50 cm height. Box coring provides immediate insight into changes within sediment sequences at different locations, e.g. from clays in the deep sea to shelf sediments, often consisting mainly of coarse ice-rafted debris (IRD) with lower amounts of fine grained material due to its winnowing. By the way, taking a box core from the Greenland shelf is tough. Not only for us, but for our equipment as well! Rocks of up to 30 kg have been recovered within some of the sediment samples.
The upcoming sampling procedure includes sampling of the surface and the pore water content, as well as the preparation of slabs for X-ray diffraction (XRD) analyses. The main purpose of a box core sampling is the recovery of core tubes and core archives for future micropaleontological, (bio)geochemical, sedimentological investigations. While sampling, one can have a nice time outside – on the deck, “playing with mud”, collecting macrofossils and peculiar sea stars from the sediment surface. Once the clouds disappear, it is really enjoyable to be outside due to the sun reflection in the waters of the North-East Greenland Polynya (where we have been for retrieving the precious mud). What is also nice here is that you do not have to be extremely lucky to see shiny sea ice floes of incredible forms and shapes. During this cruise on the RV Polarstern “the box core team” also intends to obtain some samples from the sediment-water interface, which will be used as a dataset of modern IP25 biomarker distribution. This novel proxy is applied for reconstruction of the sea ice. Thus, knowing the current position of the sea ice edge, we will have better constrains for paleoenvironmental reconstructions in this region.
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