The Enigmatic Pockmarks of the Sandy Southeastern North Sea

Christoph Böttner; Jasper J.L. Hoffmann; Daniel Unverricht; Mark Schmidt; Timo Spiegel; Jacob Geersen; Thomas Harald Müller; Jens Karstens; Katrine Juul Andresen; Lasse Sander; Jens Schneider von Deimling; Christopher Schmidt

doi:10.1029/2024GC011837

The Enigmatic Pockmarks of the Sandy Southeastern North Sea

Christoph Böttner^*, Jasper J.L. Hoffmann, Daniel Unverricht, Mark Schmidt, Timo Spiegel, Jacob Geersen, Thomas Harald Müller, Jens Karstens, Katrine Juul Andresen, Lasse Sander, Jens Schneider von Deimling, Christopher Schmidt

^*Corresponding author for this work

Department of Geoscience

Research output: Contribution to journal/Conference contribution in journal/Contribution to newspaper › Journal article › Research › peer-review

Abstract

Natural seafloor depressions, known as pockmarks, are common subaqueous geomorphological features found from the deep ocean trenches to shallow lakes. Pockmarks can form rapidly or over millions of years and have a large variety of shapes created and maintained by a large variety of mechanisms. In the sandy sediments of the southeastern North Sea, abundant shallow pockmarks are ubiquitous and occur at shallow water depths (<50 m). Their formation has previously been linked to methane seepage from the seafloor. Here, we characterize over 50,000 pockmarks based on their morphology, geochemical signature, and the subsurface pre-conditions using a new integrated geoscientific data set, combining geophysical and sedimentological data with geochemical porewater and oceanographic analysis. We test whether the methane seepage is indeed responsible for pockmark formation. However, our data suggest that neither the seepage of light hydrocarbons nor groundwater is driving pockmark formation. Because of this lack of evidence for fluid seepage, we favor the previously suggested biotic formation but also discuss positive feedback mechanisms in ocean bottom currents as a formation process. Based on a comparison of pockmarks to the central and southeastern North Sea, we find that local lithology significantly affects pockmark morphology. Muddy lithologies favor the formation of larger, long-lived structures, while sandy lithologies lead to short-lived, small-scale structures that are large in area but with shallow incision depth. We conclude that pockmarks in sandy environments might have been overlooked globally due to their shallow incision depth and recommend reevaluating the role of hydrocarbon ebullition in pockmark formation.

Original language	English
Article number	e2024GC011837
Journal	Geochemistry, Geophysics, Geosystems
Volume	25
Issue	11
ISSN	1525-2027
DOIs	https://doi.org/10.1029/2024GC011837
Publication status	Published - Nov 2024

Keywords

fluid flow
geomorphology
interdisciplinary
lithology
North Sea
pockmarks

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10.1029/2024GC011837Licence: CC BY

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title = "The Enigmatic Pockmarks of the Sandy Southeastern North Sea",

abstract = "Natural seafloor depressions, known as pockmarks, are common subaqueous geomorphological features found from the deep ocean trenches to shallow lakes. Pockmarks can form rapidly or over millions of years and have a large variety of shapes created and maintained by a large variety of mechanisms. In the sandy sediments of the southeastern North Sea, abundant shallow pockmarks are ubiquitous and occur at shallow water depths (<50 m). Their formation has previously been linked to methane seepage from the seafloor. Here, we characterize over 50,000 pockmarks based on their morphology, geochemical signature, and the subsurface pre-conditions using a new integrated geoscientific data set, combining geophysical and sedimentological data with geochemical porewater and oceanographic analysis. We test whether the methane seepage is indeed responsible for pockmark formation. However, our data suggest that neither the seepage of light hydrocarbons nor groundwater is driving pockmark formation. Because of this lack of evidence for fluid seepage, we favor the previously suggested biotic formation but also discuss positive feedback mechanisms in ocean bottom currents as a formation process. Based on a comparison of pockmarks to the central and southeastern North Sea, we find that local lithology significantly affects pockmark morphology. Muddy lithologies favor the formation of larger, long-lived structures, while sandy lithologies lead to short-lived, small-scale structures that are large in area but with shallow incision depth. We conclude that pockmarks in sandy environments might have been overlooked globally due to their shallow incision depth and recommend reevaluating the role of hydrocarbon ebullition in pockmark formation.",

keywords = "fluid flow, geomorphology, interdisciplinary, lithology, North Sea, pockmarks",

author = "Christoph B{\"o}ttner and Hoffmann, {Jasper J.L.} and Daniel Unverricht and Mark Schmidt and Timo Spiegel and Jacob Geersen and M{\"u}ller, {Thomas Harald} and Jens Karstens and Andresen, {Katrine Juul} and Lasse Sander and {Schneider von Deimling}, Jens and Christopher Schmidt",

year = "2024",

month = nov,

doi = "10.1029/2024GC011837",

language = "English",

volume = "25",

journal = "Geochemistry, Geophysics, Geosystems",

issn = "1525-2027",

publisher = "John Wiley & Sons Inc.",

number = "11",

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TY - JOUR

T1 - The Enigmatic Pockmarks of the Sandy Southeastern North Sea

AU - Böttner, Christoph

AU - Hoffmann, Jasper J.L.

AU - Unverricht, Daniel

AU - Schmidt, Mark

AU - Spiegel, Timo

AU - Geersen, Jacob

AU - Müller, Thomas Harald

AU - Karstens, Jens

AU - Andresen, Katrine Juul

AU - Sander, Lasse

AU - Schneider von Deimling, Jens

AU - Schmidt, Christopher

PY - 2024/11

Y1 - 2024/11

N2 - Natural seafloor depressions, known as pockmarks, are common subaqueous geomorphological features found from the deep ocean trenches to shallow lakes. Pockmarks can form rapidly or over millions of years and have a large variety of shapes created and maintained by a large variety of mechanisms. In the sandy sediments of the southeastern North Sea, abundant shallow pockmarks are ubiquitous and occur at shallow water depths (<50 m). Their formation has previously been linked to methane seepage from the seafloor. Here, we characterize over 50,000 pockmarks based on their morphology, geochemical signature, and the subsurface pre-conditions using a new integrated geoscientific data set, combining geophysical and sedimentological data with geochemical porewater and oceanographic analysis. We test whether the methane seepage is indeed responsible for pockmark formation. However, our data suggest that neither the seepage of light hydrocarbons nor groundwater is driving pockmark formation. Because of this lack of evidence for fluid seepage, we favor the previously suggested biotic formation but also discuss positive feedback mechanisms in ocean bottom currents as a formation process. Based on a comparison of pockmarks to the central and southeastern North Sea, we find that local lithology significantly affects pockmark morphology. Muddy lithologies favor the formation of larger, long-lived structures, while sandy lithologies lead to short-lived, small-scale structures that are large in area but with shallow incision depth. We conclude that pockmarks in sandy environments might have been overlooked globally due to their shallow incision depth and recommend reevaluating the role of hydrocarbon ebullition in pockmark formation.

AB - Natural seafloor depressions, known as pockmarks, are common subaqueous geomorphological features found from the deep ocean trenches to shallow lakes. Pockmarks can form rapidly or over millions of years and have a large variety of shapes created and maintained by a large variety of mechanisms. In the sandy sediments of the southeastern North Sea, abundant shallow pockmarks are ubiquitous and occur at shallow water depths (<50 m). Their formation has previously been linked to methane seepage from the seafloor. Here, we characterize over 50,000 pockmarks based on their morphology, geochemical signature, and the subsurface pre-conditions using a new integrated geoscientific data set, combining geophysical and sedimentological data with geochemical porewater and oceanographic analysis. We test whether the methane seepage is indeed responsible for pockmark formation. However, our data suggest that neither the seepage of light hydrocarbons nor groundwater is driving pockmark formation. Because of this lack of evidence for fluid seepage, we favor the previously suggested biotic formation but also discuss positive feedback mechanisms in ocean bottom currents as a formation process. Based on a comparison of pockmarks to the central and southeastern North Sea, we find that local lithology significantly affects pockmark morphology. Muddy lithologies favor the formation of larger, long-lived structures, while sandy lithologies lead to short-lived, small-scale structures that are large in area but with shallow incision depth. We conclude that pockmarks in sandy environments might have been overlooked globally due to their shallow incision depth and recommend reevaluating the role of hydrocarbon ebullition in pockmark formation.

KW - fluid flow

KW - geomorphology

KW - interdisciplinary

KW - lithology

KW - North Sea

KW - pockmarks

UR - http://www.scopus.com/inward/record.url?scp=85209638517&partnerID=8YFLogxK

U2 - 10.1029/2024GC011837

DO - 10.1029/2024GC011837

M3 - Journal article

AN - SCOPUS:85209638517

SN - 1525-2027

VL - 25

JO - Geochemistry, Geophysics, Geosystems

JF - Geochemistry, Geophysics, Geosystems

IS - 11

M1 - e2024GC011837

ER -

The Enigmatic Pockmarks of the Sandy Southeastern North Sea

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