Pockmarks are classically described as conical shaped seabed depressions, but can vary greatly in shape and size. It is becoming increasingly apparent that the fjordic environments of western Scotland represent a more substantial carbon store (per square metre) than terrestrial equivalents ( Smeaton et al., 2016). (2017) demonstrate that the earlier estimates of organic carbon within Scotland’s 111 fjords or ‘sea lochs’ significantly underestimated the actual total, probably by around three orders of magnitude (0.34 Mt cf 640.7 Mt of C). Two recent studies have provided the first quantitative estimates of total carbon storage buried within Scotland’s fjordic sediments ( Burrows et al., 2014 Smeaton et al., 2017) however, the results differ strongly. Despite fjordic environments being recognised over three decades ago as major carbon stores and globally important natural sequestration sites ( Syvitski, Burrell, & Skei, 1987), quantifying the carbon in fjordic and other marine sedimentary systems has remained a largely neglected topic. This work presents the first detailed mapping of pockmark fields in Scottish west coast waters and highlights the use of pockmarks as an indicator of the quantity, mobility and fate of stored carbon.įjords, firths and coastal seabed sediments are important stores of carbon ( Smeaton et al., 2016 Smith, Bianchi, Allison, Savage, & Galy, 2015). The recognition of separate pockmark classes could aid understanding of their age, activity and origin. A k-means clustering algorithm identifies three classes of pockmark morphology: deep, elongate and regular. We use morphological metrics and statistical procedures to classify and analyse the variety of pockmark forms. We map 1019 individual pockmarks in 12 different hydrographic areas covering ca. We use a Geographical Information System (GIS) to analyse multibeam echo-sounder bathymetric data and use a range of semi-automated tools to map seabed pockmarks in fjords and adjacent coastal waters around western Scotland. So, the common model for pockmark formation is not working in this site,' and more research will be required to determine what shaped these pits and pocks, Paull said at AGU.Pockmarks are seabed depressions that represent primary evidence of rapid biogenic/thermogenic gas build up and fluid release from seabed sediments to the water column. 'Both the pockmarks and the microdepressions that we found show no evidence of methane venting going on. And when they extracted sediment cores from inside the pockmarks and microdepressions and analyzed the water chemistry, they didn't find any chemical traces indicating the presence of methane or fluid. The usual explanation for seabed pits such as these is that they are formed by flows of subsurface fluids or methane gases this can create unstable conditions in the seabed that would be unsuitable for a wind farm, Paull said.īut the scientists saw no visual evidence of disturbance in the pits. What's more, the larger pockmarks haven’t changed for more than 50,000 years, Paull said.

'From what we know about the rate that sediments accumulate in this area that comes with C-14 dating, this would indicate that the strata deposited at this level were deposited 400,000 years ago, which suggests these features have persisted through time,' said Paull. 'Many have substantial accumulations of debris, trash - whole plastic bags in some cases,' Paull said. The microdepressions also contained garbage. They had steeper sides than the larger pits and had 'tails' that trailed off in one direction, hinting that currents may have played a role in their formation, Paull explained. The exceptional detail of these new views also revealed the microdepressions for the first time. The diving robot can do 10 times better, achieving 1-meter resolution, he said.Īt that higher resolution, the pockmarks were found to be smooth and nearly perfectly circular. The state-of-the-art NOAA tool can get resolution that's on the order of 10 meters. The unusual pockmarks were first mapped from the sea surface by scientists with the National Oceanic and Atmospheric Administration (NOAA), MBARI and other agencies using sonar, but examining them at high resolution required MBARI's sonar-mounted diving robots - autonomous underwater vehicles (AUV), according to Paull.

Pock me on the water