Although fishing is one of the most widespread activities by which humans harvest natural resources, its global footprint is poorly understood and has never been directly quantified. We processed 22 ...billion automatic identification system messages and tracked >70,000 industrial fishing vessels from 2012 to 2016, creating a global dynamic footprint of fishing effort with spatial and temporal resolution two to three orders of magnitude higher than for previous data sets. Our data show that industrial fishing occurs in >55% of ocean area and has a spatial extent more than four times that of agriculture. We find that global patterns of fishing have surprisingly low sensitivity to short-term economic and environmental variation and a strong response to cultural and political events such as holidays and closures.
Ending hide and seek at sea McCauley, Douglas J.; Woods, Paul; Sullivan, Brian ...
Science,
03/2016, Volume:
351, Issue:
6278
Journal Article
Peer reviewed
Open access
New technologies could revolutionize ocean observation
The ocean remains the least observed part of our planet. This deficiency was made obvious by two recent developments in ocean governance: the ...emerging global movement to create massive marine protected areas (MPAs) (
1
) and a new commitment by the United Nations (UN) to develop a legally binding treaty to better manage high-seas biodiversity (
2
). Both policy goals cause us to confront whether it is meaningful to legislate change in ocean areas that we have little capacity to observe transparently. Correspondingly, there has been a surge in interest in the potential of publicly accessible data from automatic ship identification systems (AIS) to fill gaps in ocean observation. We demonstrate how AIS data can be used to empower and propel forward a new era of spatially ambitious marine governance and research. The value of AIS, however, is inextricably linked to the strength of policies by which it is backed.
Amoroso
demonstrate the power of our data by estimating the high-resolution trawling footprint on seafloor habitat. Yet we argue that a coarser grid is required to understand full ecosystem impacts. ...Vessel tracking data allow us to estimate the footprint of human activities across a variety of scales, and the proper scale depends on the specific impact being investigated.
The recent availability of a terrestrial high-resolution digital elevation model in Sweden has led to the discovery of previously unknown scarps believed to be associated with bedrock faults that ...ruptured to the surface during the Holocene. Field investigations, however, are required to confirm these findings and determine the timing of post-glacial seismicity. Here, we present results from a unique hybrid approach, where hydroacoustical data from the sediments of Lake Voxsjön are compared to stratigraphic and geomorphologic records from nearby terrestrial settings. The hydroacoustical data are largely consistent with the terrestrial data indicating a single fault rupture shortly after deglaciation, which occurred about 11,000–10,500 cal BP.
We have found that the extensively used finite difference scheme time3d produces time fields which are ‘asymmetric’ in the sense that traveltimes computed to the right of the source are faster than ...traveltimes computed to the left. All finite difference schemes will, as they are approximations to the wave equation, to some extent fail to obey reciprocity perfectly. We show, however, that the errors in time3d may be significant—and unnecessarily large. An asymmetry in the point source initialization has been identified, and after correction time3d produces time fields with an improved reciprocity.
MARINE GOVERNANCE. Ending hide and seek at sea McCauley, Douglas J; Woods, Paul; Sullivan, Brian ...
Science (American Association for the Advancement of Science),
2016-Mar-11, 20160311, Volume:
351, Issue:
6278
Journal Article
When seismic profiles deviate significantly from straight lines, the results from 2D traveltime inversion programs will be in error due to the inherent 3D component present in the data. Thus, it is ...necessary to use a program that can handle the 3D aspects of the acquisition geometry. This study compares the performance and results from two computer programs for 3D seismic tomography. These algorithms are the package for
First
Arrival
Seismic
Tomography (FAST) and a Local Earthquake tomography program, PStomo_eq. Although both codes invert for the velocity field using the conjugate gradient solver LSQR, the common smoothness constraint is handled differently. In addition, the programs do not incorporate the same options for user-specified constraints. These differences in implementation are clearly observed in the inverted velocity fields obtained in this study. Both FAST and PStomo_eq are applied to synthetic and real data sets with crooked line geometry. First arrival traveltimes from seismic data acquired in the Siljan ring impact area are used for the real data set test. The results show that FAST gives smoother models than PStomo_eq. On the real data set PStomo_eq showed a better correlation to the information at hand. Different criteria exist for what is desirable in a model; thus, the choice of which program to use will mostly depend on the particular goals of the study.
A major cost in exploring the upper 1–2 km of crystalline crust with reflection seismics is the drilling required for explosive sources. By reducing the charge size to a minimum, shallow inexpensive ...shotholes can be drilled with handheld equipment. Here, we present results from a full-scale test using small charges for high-resolution seismic surveying over a nuclear waste disposal study site (not an actual site). Two 2–2.5-km-long crossing profiles were acquired in December 1999 with 10-m shot and geophone spacing in the Laxemar area, near Oskarshamn in southeastern Sweden. After standard processing, including dip moveout (DMO), several subhorizontal to moderately dipping reflections are imaged. Many of the dipping ones can be correlated to fracture zones observed in a ca. 1700-m-deep borehole where the profiles cross and/or to fracture zones mapped on the surface. The imaged fracture zones form a complex 3D pattern illustrating the necessity of having 3D control before interpreting seismic reflection data. Analyses of sonic and density logs from the borehole show that greenstones have significantly higher impedances than the more dominant granite found in the borehole (granite/greenstone reflection coefficient is +0.065). These greenstones may contribute to the reflectivity when associated with fracture zones. In some cases, where they are present as larger subhorizontal lenses, they may be the dominant source of reflectivity. A set of north-dipping (10°) reflectors at 3–3.5-km depth can be correlated to a similar set observed below the island of Ävrö about 3 km to the east.
Reflection seismic and seismic tomography methods can be used to image the upper kilometer of hard bedrock and the loose unconsolidated sediments covering it. Developments of these two methods and ...their application, as well as identifying issues concerning their usage, are the main focus of the thesis. Data used for this development were acquired at three different sites in Sweden, in Forsmark 140 km north of Stockholm, in the Oskarshamn area in southern Sweden, and in the northern part of the Siljan Ring impact crater area.
The reflection seismic data were acquired with long source-receiver offsets relative to some of the targeted depths to be imaged. In the initial processing standard steps were applied, but the uppermost part of the sections were not always clear. The longer offsets imply that pre-stack migration is necessary in order to image the uppermost bedrock as clearly as possible. Careful choice of filters and velocity functions improve the pre-stack migrated image, allowing better correlation with near-surface geological information.
The seismic tomography method has been enhanced to calculate, simultaneously with the velocity inversion, optimal corrections to the picked first break travel times in order to compensate for the delays due to the seismic waves passing through the loose sediments covering the bedrock.
The reflection seismic processing used in this thesis has produced high-quality images of the upper kilometers, and in one example from the Forsmark site, the image of the uppermost 250 meters of the bedrock has been improved. The three-dimensional orientation of reflections has been determined at the Oskarshamn site. Correlation with borehole data shows that many of these reflections originate from fracture zones.
The developed seismic tomography method produces high-detail velocity models for the site in the Siljan impact area and for the Forsmark site. In Forsmark, detailed estimates of the bedrock topography were calculated with the use of the developed tomography method.
Härtill 4 uppsatser
Diss. (sammanfattning) Uppsala : Uppsala universitet, 2005
filosofie doktorsexamen
Doctor philosophiae
degree of Doctor of Philosophy
Docteur ès lettres
Axel Hambergsalen, Geocentrum, Villavägen 16, Uppsala
Härtill 4 uppsatser
Diss. (sammanfattning) Uppsala : Uppsala universitet, 2005
filosofie doktorsexamen
Doctor philosophiae
Axel Hambergsalen, Geocentrum, Villavägen 16, Uppsala
Reflection seismic and seismic tomography methods can be used to image the upper kilometer of hard bedrock and the loose unconsolidated sediments covering it. Developments of these two methods and their application, as well as identifying issues concerning their usage, are the main focus of the thesis. Data used for this development were acquired at three different sites in Sweden, in Forsmark 140 km north of Stockholm, in the Oskarshamn area in southern Sweden, and in the northern part of the Siljan Ring impact crater area.
The reflection seismic data were acquired with long source-receiver offsets relative to some of the targeted depths to be imaged. In the initial processing standard steps were applied, but the uppermost part of the sections were not always clear. The longer offsets imply that pre-stack migration is necessary in order to image the uppermost bedrock as clearly as possible. Careful choice of filters and velocity functions improve the pre-stack migrated image, allowing better correlation with near-surface geological information.
The seismic tomography method has been enhanced to calculate, simultaneously with the velocity inversion, optimal corrections to the picked first break travel times in order to compensate for the delays due to the seismic waves passing through the loose sediments covering the bedrock.
The reflection seismic processing used in this thesis has produced high-quality images of the upper kilometers, and in one example from the Forsmark site, the image of the uppermost 250 meters of the bedrock has been improved. The three-dimensional orientation of reflections has been determined at the Oskarshamn site. Correlation with borehole data shows that many of these reflections originate from fracture zones.
The developed seismic tomography method produces high-detail velocity models for the site in the Siljan impact area and for the Forsmark site. In Forsmark, detailed estimates of the bedrock topography were calculated with the use of the developed tomography method.
degree of Doctor of Philosophy
Docteur ès lettres
Reflection seismic and seismic tomography methods can be used to image the upper kilometer of hard bedrock and the loose unconsolidated sediments covering it. Developments of these two methods and ...their application, as well as identifying issues concerning their usage, are the main focus of the thesis. Data used for this development were acquired at three different sites in Sweden, in Forsmark 140 km north of Stockholm, in the Oskarshamn area in southern Sweden, and in the northern part of the Siljan Ring impact crater area. The reflection seismic data were acquired with long source-receiver offsets relative to some of the targeted depths to be imaged. In the initial processing standard steps were applied, but the uppermost part of the sections were not always clear. The longer offsets imply that pre-stack migration is necessary in order to image the uppermost bedrock as clearly as possible. Careful choice of filters and velocity functions improve the pre-stack migrated image, allowing better correlation with near-surface geological information. The seismic tomography method has been enhanced to calculate, simultaneously with the velocity inversion, optimal corrections to the picked first break travel times in order to compensate for the delays due to the seismic waves passing through the loose sediments covering the bedrock. The reflection seismic processing used in this thesis has produced high-quality images of the upper kilometers, and in one example from the Forsmark site, the image of the uppermost 250 meters of the bedrock has been improved. The three-dimensional orientation of reflections has been determined at the Oskarshamn site. Correlation with borehole data shows that many of these reflections originate from fracture zones. The developed seismic tomography method produces high-detail velocity models for the site in the Siljan impact area and for the Forsmark site. In Forsmark, detailed estimates of the bedrock topography were calculated with the use of the developed tomography method.
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