Accumulation of organic carbon in Baffin Bay and Labrador Sea sediments (ODP-Leg 105)

Abstract. Reconstructing the opening of the Labrador Sea and Baffin Bay between Greenland and North America remains controversial. Recent seismic data suggest that magnetic lineations along the margins of the Labrador Sea, originally interpreted as seafloor spreading anomalies, may lie within the crust of the continent–ocean transition. These data also suggest a more seaward extent of continental crust within the Greenland margin near the Davis Strait than assumed in previous full-fit reconstructions. Our study focuses on reconstructing the full-fit configuration of Greenland and North America using an approach that considers continental deformation in a quantitative manner. We use gravity inversion to map crustal thickness across the conjugate margins, and assimilate observations from available seismic profiles and potential field data to constrain the likely extent of different crustal types. We derive end-member continental margin restorations following alternative interpretations of published seismic profiles. The boundaries between continental and oceanic crust (COB) are restored to their pre-stretching locations along small circle motion paths across the region of Cretaceous extension. Restored COBs are fitted quantitatively to compute alternative total-fit reconstructions. A preferred full-fit model is chosen based on the strongest compatibility with geological and geophysical data. Our preferred model suggests that (i) the COB lies oceanward of magnetic lineations interpreted as magnetic anomaly 31 (70 Ma) in the Labrador Sea, (ii) all previously identified magnetic lineations landward of anomaly 27 reflect intrusions into continental crust, and (iii) the Ungava fault zone in Davis Strait acted as a leaky transform fault during rifting. This robust plate reconstruction reduces gaps and overlaps in the Davis Strait and suggests that there is no need for alternative models proposed for reconstructions of this area including additional plate boundaries in North America or Greenland. Our favored model implies that break up and formation of continent–ocean transition (COT) first started in the southern Labrador Sea and Davis Strait around 88 Ma and then propagated north and southwards up to onset of real seafloor spreading at 63 Ma in the Labrador Sea. In the Baffin Bay, continental stretching lasted longer and actual break up and seafloor spreading started around 61 Ma (Chron 26).

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Isotopic evidence for changes in the origin and cycling of nitrogen in the Labrador Sea during the last 8,000 years

10.5194/egusphere-egu2020-12134 ◽

2020 ◽

Author(s):

Markus Kienast ◽

Sam Davin ◽

Kristin Doering ◽

Dierk Hebbeln ◽

Stephanie Kienast ◽

...

Keyword(s):

Nitrogen Fixation ◽

Water Column ◽

North Atlantic ◽

North Pacific ◽

Isotopic Signature ◽

Labrador Sea ◽

Nitrate Sources ◽

Baffin Bay ◽

The North ◽

The North Atlantic

Subsurface nitrate in the Labrador Sea (NW Atlantic) and Baffin Bay is provided by North Pacific water flowing through Bering Strait and the Canadian Arctic as well as by advection from the North Atlantic. Both these nitrate sources are distinct in their isotopic signature (&#948;15N), owing to benthic denitrification on the Bering, Chukchi and east Siberian shelves and nitrogen fixation in the North Atlantic, respectively. Accordingly, water column profiles of &#948;15N(nitrate) collected off Greenland in the eastern Labrador Sea show low &#948;15N(nitrate), which mixes with more 15N-enriched nitrate flowing through Baffin Bay into the northern Labrador Sea. The Labrador Current carries this mixture southward along the western Labrador Sea, toward Newfoundland. The &#948;15N of surface sediments in the Labrador Sea closely mirrors these water column signals, suggesting that sediments can be used to trace changes in both the source signature of Atlantic versus Pacific-derived nitrate as well as in the admixture of the two source waters.Two downcore sedimentary &#948;15N records from the NE and NW Labrador Sea coast both show high &#948;15N values of ca. 7&#8240; during the early Holocene (9-7 kyrs BP). In the NE Labrador Sea, this is followed by a long-term decrease toward &#948;15N of ca. 4.5&#8240; at the core top, in contrast to a much more subtle decrease in the NW Labrador Sea (surface sediment &#948;15N of ca. 6.5&#8240;). The decreasing &#948;15N values along the eastern Labrador Sea are consistent with a Holocene increase in nitrogen fixation in the North Atlantic or an increasing advection of isotopically light nitrate. In turn, an increasing admixture of North-Pacific-derived nitrate, or intensified denitrification on the Bering Shelf would be required to explain the much subdued Holocene &#948;15N decrease in the NW Labrador Sea.

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The Arctic Dredge, a Benthic Biological Sampler for Mixed Boulder and Mud Substrates

Journal of the Fisheries Research Board of Canada ◽

10.1139/f72-235 ◽

1972 ◽

Vol 29 (10) ◽

pp. 1503-1505 ◽

Cited By ~ 2

Author(s):

A. H. Clarke

Keyword(s):

Single Point ◽

The Arctic ◽

Labrador Sea ◽

Baffin Bay ◽

Reliable Tool ◽

Specimen Retrieval

Benthic biological dredges of a new design have been used successfully on ice-rafted archibenthal and abyssal sediments of boulders and mud. The dredge is kite-shaped, of massive construction, and features a single point for cable attachment and a removable cannister for specimen retrieval. Experience in Baffin Bay, the Labrador Sea, and the Icelandic Shelf indicates that the arctic dredge is a reliable tool for arctic and subarctic research.

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