Martin Jakobsson

The International Bathymetric Chart of the Arctic Ocean (IBCAO) Version 3.0

The International Bathymetric Chart of the Arctic Ocean (IBCAO) released its first gridded bathymetric compilation in 1999. The IBCAO bathymetric portrayals have since supported a wide range of Arc ...

The Cenozoic palaeoenvironment of the Arctic Ocean

The history of the Arctic Ocean during the Cenozoic era (0–65 million years ago) is largely unknown from direct evidence. Here we present a Cenozoic palaeoceanographic record constructed from >400 m of sediment core from a recent drilling expedition to the Lomonosov ridge in the Arctic Ocean. Our record shows a palaeoenvironmental transition from a warm ‘greenhouse’ world, during the late Palaeocene and early Eocene epochs, to a colder ‘icehouse’ world influenced by sea ice and icebergs from the middle Eocene epoch to the present. For the most recent ∼14 Myr, we find sedimentation rates of 1–2 cm per thousand years, in stark contrast to the substantially lower rates proposed in earlier studies; this record of the Neogene reveals cooling of the Arctic that was synchronous with the expansion of Greenland ice (∼3.2 Myr ago) and East Antarctic ice (∼14 Myr ago). We find evidence for the first occurrence of ice-rafted debris in the middle Eocene epoch (∼45 Myr ago), some 35 Myr earlier than previously thought; fresh surface waters were present at ∼49 Myr ago, before the onset of ice-rafted debris. Also, the temperatures of surface waters during the Palaeocene/Eocene thermal maximum (∼55 Myr ago) appear to have been substantially warmer than previously estimated. The revised timing of the earliest Arctic cooling events coincides with those from Antarctica, supporting arguments for bipolar symmetry in climate change.

New grid of Arctic bathymetry aids scientists and mapmakers

For over two decades, Sheet 5.17 of the Fifth Edition of the General Bathymetric Chart of the Oceans (GEBCO) [Canadian Hydrographic Service, 1979] has been considered the authoritative portrayal of the sea floor north of 64 N.This sheet was constructed from publicly available bathymetric data sets, which in the late 1970s were rather sparse, consisting almost entirely of underway measurements collected from ice-breakers, drifting ice islands, and point measurements obtained along snow-mobile tracks or using air support. Data coverage tended to be fairly good at lower latitudes where ice cover was not a hindrance, but at higher latitudes, where ice was more prevalent, major features such as the Amerasian and Eurasian Basins were not well delineated. This situation posed problems not only for expedition planners but also for scientific investigators, who needed an accurate description of the sea floor to design field experiments and to link their research with processes affecting or affected by the shape of the seabed (for example, sea level change, ocean circulation, sediment transport,seafloor spreading, and Pleistocene glaciation).

The early Miocene onset of a ventilated circulation regime in the Arctic Ocean.

Deep-water formation in the northern North Atlantic Ocean and the Arctic Ocean is a key driver of the global thermohaline circulation and hence also of global climate. Deciphering the history of the circulation regime in the Arctic Ocean has long been prevented by the lack of data from cores of Cenozoic sediments from the Arctic’s deep-sea floor. Similarly, the timing of the opening of a connection between the northern North Atlantic and the Arctic Ocean, permitting deep-water exchange, has been poorly constrained. This situation changed when the first drill cores were recovered from the central Arctic Ocean. Here we use these cores to show that the transition from poorly oxygenated to fully oxygenated (‘ventilated’) conditions in the Arctic Ocean occurred during the later part of early Miocene times. We attribute this pronounced change in ventilation regime to the opening of the Fram Strait. A palaeo-geographic and palaeo-bathymetric reconstruction of the Arctic Ocean, together with a physical oceanographic analysis of the evolving strait and sill conditions in the Fram Strait, suggests that the Arctic Ocean went from an oxygen-poor ‘lake stage’, to a transitional ‘estuarine sea’ phase with variable ventilation, and finally to the fully ventilated ‘ocean’ phase 17.5 Myr ago. The timing of this palaeo-oceanographic change coincides with the onset of the middle Miocene climatic optimum, although it remains unclear if there is a causal relationship between these two events.

Ice shelves in the Pleistocene Arctic Ocean inferred from glaciogenic deep-sea bedforms

It has been proposed that during Pleistocene glaciations, an ice cap of 1 kilometre or greater thickness covered the Arctic Ocean. This notion contrasts with the prevailing view that the Arctic Ocean was covered only by perennial sea ice with scattered icebergs. Detailed mapping of the ocean floor is the best means to resolve this issue. Although sea-floor imagery has been used to reconstruct the glacial history of the Antarctic shelf , little data have been collected in the Arctic Ocean because of operational constraints. The use of a geophysical mapping system during the submarine SCICEX expedition in 1999 provided the opportunity to perform such an investigation over a large portion of the Arctic Ocean. Here we analyse backscatter images and sub-bottom profiler records obtained during this expedition from depths as great as 1 kilometre. These records show multiple bedforms indicative of glacial scouring and moulding of sea floor, combined with large-scale erosion of submarine ridge crests. These distinct glaciogenic features demonstrate that immense, Antarctic-type ice shelves up to 1 kilometre thick and hundreds of kilometres long existed in the Arctic Ocean during Pleistocene glaciations.

Manganese and color cycles in Arctic Ocean sediments constrain Pleistocene chronology

Sequential variations in manganese (Mn) content and color of deepsea sediments retrieved from the Lomonosov Ridge (87°N) in the central Arctic Ocean apparently mimic low-latitude δ 18 O glacial-interglacial cyclicity, thereby providing stratigraphic information that together with biostratigraphic data permit the construction of a detailed chronological model. Correlation of this Mn and color chronology to established apparent Brunhes-age estimates of geomagnetic excursions reveals a remarkable fit between these two independently derived time scales. The Mn and color cycles probably provide paleoenvironmental information about material fluxes in the Arctic Ocean over the past 1 m.y. We suggest that the primary source for the observed manganese variations in our sediment core is northern Siberia, which has extensive peat bogs and boreal forests. These Siberian source areas could operate in an off and on mode tuned to Pleistocene glacial and interglacial periods. Contrasts in ventilation of Arctic Ocean waters during interglacial-glacial cycles probably could also enhance the observed Mn and color variability.

Age model and core‐seismic integration for the Cenozoic Arctic Coring Expedition sediments from the Lomonosov Ridge

Cenozoic biostratigraphic, cosmogenic isotope, magnetostratigraphic, and cyclostratigraphic data derived from Integrated Ocean Drilling Program Expedition 302, the Arctic Coring Expedition (ACEX), are merged into a coherent age model. This age model has low resolution because of poor core recovery, limited availability of biostratigraphic information, and the complex nature of the magnetostratigraphic record. One 2.2 Ma long hiatus occurs in the late Miocene; another spans 26 Ma (18.2–44.4 Ma). The average sedimentation rate in the recovered Cenozoic sediments is about 15 m/Ma. Core-seismic correlation links the ACEX sediments to the reflection seismic stratigraphy of line AWI-91090, on which the ACEX sites were drilled. This seismostratigraphy can be correlated over wide geographic areas in the central Arctic Ocean, implying that the ACEX age model can be extended well beyond the drill sites.

Pleistocene stratigraphy and paleoenvironmental variation from Lomonosov Ridge sediments, central Arctic Ocean

Abstract High resolution seismoacoustic chirp sonar data and piston cores were collected from the Lomonosov Ridge in the central Arctic Ocean (85°–90°N; 130°–155°E). The chirp sonar data indicate substantial erosion on the ridge crest above 1000 mbsl while data from deeper sites show apparently undisturbed sedimentation. Piston cores from both the eroded ridge crest and the slopes have been analyzed for a variety of properties, permitting inter-core correlation and description of paleoenvironmental change over time. Based on the evidence of extensive sediment erosion at depths above 1000 mbsl, we infer that the top of the Lomonosov Ridge has been eroded by grounded ice during a prominent glacial event that took place during MIS 6 according to a newly published age model. This event is coeval with a dramatic shift from low amplitude glacial–interglacial variability to high amplitude variability recorded in the sedimentary record. The new age model used in our study is based on nannofossil biostratigraphy and correlation between sedimentary cycles and a low-latitude oxygen isotope record and confirmed by paleomagnetic polarity studies where negative paleomagnetic inclinations are assigned to excursions. Due to the controversy between this age model and age models that assign the negative paleomagnetic inclinations to polarity reversals, we provide a correlation to Lomonosov Ridge core PS2185-6 [Spielhagen et al., Geology, 25 (1997) 783]. According to the latter age models, the Lomonosov Ridge was eroded by ice grounding much earlier, at MIS 16.

Mid-Cenozoic tectonic and paleoenvironmental setting of the central Arctic Ocean

Drilling results from the Integrated Ocean Drilling Program’s Arctic Coring Expedition (ACEX) to the Lomonosov Ridge (LR) document a 26 million year hiatus that separates freshwater-influenced biosilica-rich deposits of the middle Eocene from fossil-poor glaciomarine silty clays of the early Miocene. Detailed micropaleontological and sedimentological data from sediments surrounding this mid-Cenozoic hiatus describe a shallow water setting for the LR, a finding that conflicts with predrilling seismic predictions and an initial postcruise assessment of its subsidence history that assumed smooth thermally controlled subsidence following rifting. A review of Cenozoic tectonic processes affecting the geodynamic evolution of the central Arctic Ocean highlights a prolonged phase of basin-wide compression that ended in the early Miocene. The coincidence in timing between the end of compression and the start of rapid early Miocene subsidence provides a compelling link between these observations and similarly accounts for the shallow water setting that persisted more than 30 million years after rifting ended. However, for much of the late Paleogene and early Neogene, tectonic reconstructions of the Arctic Ocean describe a landlocked basin, adding additional uncertainty to reconstructions of paleodepth estimates as the magnitude of regional sea level variations remains unknown.

A new digital bathymetric model of the world's oceans

General Bathymetric Chart of the Oceans (GEBCO) has released the GEBCO_2014 grid, a new digital bathymetric model of the world ocean floor merged with land topography from publicly available digital elevation models. GEBCO_2014 has a grid spacing of 30 arc seconds, and updates the 2010 release (GEBCO_08) by incorporating new versions of regional bathymetric compilations from the International Bathymetric Chart of the Arctic Ocean (IBCAO), the International Bathymetric Chart of the Southern Ocean (IBCSO), the Baltic Sea Bathymetry Database (BSBD), and data from the European Marine Observation and Data network (EMODnet) bathymetry portal, among other data sources. Approximately 33% of ocean grid cells (not area) have been updated in GEBCO_2014 from the previous version, including both new interpolated depth values and added soundings. These updates include large amounts of multibeam data collected using modern equipment and navigation techniques, improving portrayed details of the world ocean floor. Of all non-land grid cells in GEBCO_2014, approximately 18% are based on bathymetric control data, i.e., primarily multibeam and single beam soundings, or pre-prepared grids which may contain some interpolated values. The GEBCO_2014 grid has a mean and median depth of 3897 m and 3441 m, respectively. Hypsometric analysis reveals that 50% of the Earths surface is comprised of seafloor located 3200 m below mean sea level, and that ~900 ship-years of surveying would be needed to obtain complete multibeam coverage of the worlds oceans.