Deep Baffin Bay Research Articles

Using Radiocarbon Measurements of Dissolved Inorganic Carbon to Determine a Revised Residence Time for Deep Baffin Bay

The Canadian Arctic is warming at three times the rate of the rest of the planet and the effects of climate change on the Arctic marine carbon cycle remains unconstrained. Baffin Bay is a semi-enclosed, Arctic basin that connects the Arctic Ocean to the north to the Labrador Sea to the south. While the physical oceanography of surface Baffin Bay is well characterized, less is known about deep water formation mechanisms within the Basin. Only a few residence-time estimates for Baffin Bay Deep Water (BBDW) exist and range from 20 to 1450 years. Better residence time estimates are needed to understand the oceanographic significance of Baffin Bay. Here we report stable carbon (δ13C) and radiocarbon (Δ14C) values of dissolved inorganic carbon (DIC) collected aboard the CCGS Amundsen in 2019. DIC δ13C and Δ14C values between ranged between -0.7‰ to +1.9‰ and -90.0‰ to +29.8‰, respectively. Surface DIC δ13C values were between +0.7‰ to +1.9‰, while deep (>100m) values were 0.0 to -0.7‰. Surface DIC Δ14C values ranged between -5.4‰ to +22.9‰, while deep DIC (>1400m) DIC Δ14C averaged -82.2 ± 8.5‰ (n = 9). To constrain natural DIC Δ14C values, we quantified the amount of atmospheric “bomb” 14C in DIC (Δ14Cbomb; using the potential alkalinity method; Palk) and anthropogenic DIC (DICanth; using the ΔC* method). Both proxies indicate an absence of Δ14Cbomb and DICanth below 1000m. Using two previously proposed deep water formation mechanisms and our corrected DIC Δ14Cnatural values, we estimated a 14C-based residence time of 360-690 years for BBDW. Based on these residence times, we infer carbon is likely stored for centuries in deep Baffin Bay.

Dissolved iron and manganese in the Canadian Arctic Ocean: On the biogeochemical processes controlling their distributions

Dissolved iron (DFe) and manganese (DMn) are essential micronutrients involved in vital phytoplankton physiological pathways, and their deficit can limit primary production in otherwise nutrient-replete surface ocean waters. In this work we present the spatial distributions and biogeochemical cycling of these metals across the Canadian GEOTRACES transect in the Canadian Arctic Ocean during the summer and autumn of 2015. Surface concentrations are dominated by freshwater inputs showing a strong negative correlation with salinity, especially for DMn which behaves more conservatively than DFe. The highest surface concentrations were measured in the Canadian Arctic Archipelago (Fe: 0.401–1.91 and Mn: 4.33–9.54 nmol kg−1) and the Canada Basin (Fe: 0.225–0.479 and Mn: 3.93–7.02 nmol kg−1), regions highly influenced by riverine inputs, whereas the lowest values were found in the Labrador Sea (Fe: 0.106–0.362 and Mn: 0.450–1.09 nmol kg−1) where freshwater inputs diminished and phytoplankton uptake increased. Subsurface and deep water distributions for both metals are largely controlled by a complex balance between sources (advective inputs and organic matter remineralization) and removal processes. The subsurface peaks (∼100–300 m) observed in the Canada Basin (Fe: 0.541 ± 0.060 and Mn: 1.38 ± 0.42 nmol kg−1) and Baffin Bay (Fe: 0.753–1.03 nmol kg−1) were advected from the Chukchi Sea and the Canadian Arctic Archipelago respectively, where DFe and DMn are released from the benthic boundary layer in these shelf-dominated environments. Advective sources associated with the Arctic Circumpolar Boundary Current, rather than vertical fluxes of DFe and DMn in sinking particles, dominate metal distributions in the deep Canada Basin waters (>300 m). In the highly productive Baffin Bay and the Labrador Sea, organic matter remineralization is a notable source of DFe and DMn to deep waters. In the deepest waters (>1000 m), scavenging of DFe and DMn govern their vertical distributions; a pseudo-first order scavenging model explained the continuous removal of DMn in the Canada Basin, where the concentrations reach uniformly low concentrations (0.150 ± 0.004 nmol kg−1) after ∼400 years. Applying this DMn scavenging model we were able to estimate the age (120–190 years) of deep Baffin Bay waters, a topic of discussion for many years.

Remote Western Arctic Nutrients Fuel Remineralization in Deep Baffin Bay

AbstractThe oceanic nitrogen cycle is critically important for the partitioning of greenhouse gases between ocean and atmosphere. Baffin Bay connects ocean regions that are major sources (North Atlantic) and sinks (North Pacific and western Arctic) of biologically available nitrogen and further harbors supersaturation of nitrous oxide and a coincident deficit in nitrate in the deep basin. Isotopic tracer profiles of both nitrogen species presented here provide novel insights into the origin and cycling of reactive nitrogen in Baffin Bay, highlighting the connectivity between different Arctic systems and horizontal components of basin‐scale nutrient transport. Baffin Bay bottom water properties are derived from export production in northern Baffin Bay, which is largely fueled by Pacific‐derived nutrients. In situ remineralization at depth gives rise to benthic denitrification, evidenced by a pronounced accumulation of nitrous oxide with a distinctively high site preference (<44‰) in the deep basin. Nutrients supplied to Baffin Bay are hence stripped from surface waters and trapped at depth over long timescales, where sedimentary denitrification further adds to the N removal capacity of the Arctic Ocean.

U- and Th-series isotopes in deep Baffin Bay sediments: Tracers of detrital sources and of contrasted glacial/interglacial sedimentary processes

Abstract Uranium (U) and thorium (Th) series have been used to document the sedimentary sources, processes and fluxes of the last ~ 115 ka in central Baffin Bay, a major gateway between the Arctic Ocean and the North Atlantic Ocean, which has been fed throughout the last ice age by sediments and meltwaters from the northeastern Laurentide Ice Sheet, the Innuitian Ice Sheet and the western Greenland Ice Sheet. Measurements have been made with a ~ 1.6 ka time resolution in sedimentary core HU2008-029-016PC (70°27′N, 64°39′W; 2063 m water depth). The lack of correlation between U-concentration, 234 U/ 238 U activity ratio (( 234 U/ 238 U) AR ), organic carbon and redox sensitive elements suggests minimum early diagenetic U-uptake if any, likely due to very low organic matter sedimentary fluxes in such a subarctic environment. Throughout the last glaciation, U- and Th-concentrations and their mass ratio, as well as ( 234 U/ 238 U) AR , do not show either any unequivocal linkage with detrital dolomitic carbonate and/or detrital silicate fluxes. Data rather suggest sedimentary supplies with singular U- and Th-series signatures linked to specific glacial margin/ice streaming events and highlighting the diversity of sedimentary sources surrounding this small oceanic basin. Large surplus of 230 Th (( 230 Th xs ) 0 ), well above the production from dissolved-U decay in the overlying water column, are observed throughout the last glacial interval in response to sediment focusing and high-sedimentation rates in the deepest part of the Bay. During this interval, high-frequency fluctuations in ( 230 Th xs ) 0 indicate either a similar variability in sedimentation rates, not captured by the age model used, and/or grain size or mineralogical-dependent 230 Th xs -scavenging rates. In the much lower sedimentation rate Holocene core–top section, the ( 230 Th xs ) 0 -inventory falls below production in the overlying water column, despite evidence for some primary productivity revival as suggested by the higher organic carbon content. 230 Th xs -losses through lateral advection via Baffin Bay water-masses overflowing through Davis Strait might account for this pattern, pointing to ocean circulation drastically differing from that of the glacial interval.

Late Quaternary chronostratigraphic framework of deep Baffin Bay glaciomarine sediments from high‐resolution paleomagnetic data

The late Quaternary Baffin Bay sediments provide exclusive records of Greenland, Innuitian and Laurentide ice sheet margin activities, as well as information about the Arctic and northern Atlantic ocean linkages through the Canadian Arctic Archipelago. Because of specific oceanographic conditions, foraminiferal δ18O‐stratigraphies and radiocarbon ages fail to provide reliable chronologies. Here we propose an original chronostratigraphy spanning the last glacial cycle based on high‐resolution paleomagnetic investigations on a 741‐cm long core (HU2008‐029‐016PC) raised from the deep central Baffin Bay, near ODP site 645. Two major difficulties were encountered: (1) the high‐frequency occurrence of rapidly deposited layers related to short ice sheet margin events (e.g., ice surges), and (2) the magnetic grain size variability. Physical and magnetic mineralogical properties were used to screen out unreliable magnetic sediment layers. The obtained relative paleointensity (RPI) proxy matches reference paleomagnetic stacks and regional records. Moreover, the resulting record depicts two major excursions which were assigned to the Laschamp and the Norwegian‐Greenland‐Sea events. It has thus been possible to derive a robust 115 ka chronology for the cored sequence. We concluded that even under such a dynamic sedimentary regime, magnetic properties of the sediments can provide a reliable chronostratigraphy, together with information on sedimentary processes.

Tectonic evolution of southern Baffin Bay and Davis Strait: Results from a seismic refraction transect between Canada and Greenland

Wide‐angle reflection/refraction seismic data were acquired on a 450‐km‐long transect in southern Baffin Bay extending from Baffin Island to Greenland. Dense air gun shots were recorded on 22 ocean bottom seismometers. APwave velocity model was developed from forward and inverse modeling of the observed travel times. Beneath the Baffin Island shelf, a three‐layered continental crust is observed with velocities of 5.5 to 6.9 km/s. Typical for transform margins, there is a sharp transition between continental and oceanic crust. Off Baffin Island, 7‐km‐thick oceanic crust is interpreted to lie in a major transform fault identified on the gravity map. Beneath the deep Baffin Bay basin, 9‐km‐thick oceanic crust is encountered but thins to 6 km within an assumed fracture zone. The thicker than normal oceanic crust indicates an ample magma supply, possibly related to melt extracted from a mantle plume. Seaward of the Greenland continental crust, 20‐km‐thick igneous crust (6.3 to 7.3 km/s) is encountered in a 25‐km‐wide zone interpreted as a leaky transform fault that can be correlated southward through Davis Strait. The igneous crust is bounded by a 20‐km wide basin to the west, underlain by 4‐km‐thick crust of unknown affinity. This structure is probably associated with transform movements. A high‐velocity lower crustal layer (7.1 km/s) of 8 km thickness is indicated beneath the Greenland crust and can be correlated into the adjacent thick igneous crust. Both the thick igneous and Greenland crust are covered by up to 4 km of Paleogene volcanics (5.2 to 5.7 km/s).

Palynostratigraphy and chronostratigraphy of Baffin Bay deep sea cores: Climatostratigraphic implications

Palynostratigraphic considerations and 14C dates (AMS; accelerator mass spectrometry) on foraminifera samples from piston cores suggest sedimentation rates as high as ca. 8–11 cm/ka in deep Baffin Bay during the Late Pleistocene. Throughout this interval Baffin Bay experiences rigorous conditions and probably the extension of a dense sea-ice cover unfavourable to phytoplanktonic productivity: the dinocyst microflora indicates only brief episodes of higher productivity related to Arctic conditions and to moderately low salinites (ca. 30–31ℵ). The abundance of reworked pre-Quaternary palynomorphs in the deposits is interpreted as a response to glacial and glacio-marine activity in the northernmost areas surrounding Baffin Bay. The dinocyst stratigraphy spanning approximately over the last ice age (ca. 100 ka) reveals that Baffin Bay constituted a confined basin, isolated from the North Atlantic Ocean, prior to the present “Interglacial”.

Grain-size variations in North Atlantic non-carbonate sediments and sources of terrigenous components

Fine-silt to medium-sand grain-size spectra of the carbonate-free fractions of 115 sea bed samples from the northern North Atlantic, the Labrador Sea and Baffin Bay can be explained as mixtures of five distinct end-members. The five end-members resemble combinations of grain-size modes which are characteristic of till-matrix (Dreimanis and Vagners, 1972). Therefore the ultimate source of most of the terrigenous deep-sea sediments in the study area is probably the veneer of glacial comminution products on the surrounding continents. Three sand-rich end-members exhibit patterns of distribution that are largely compatible with the modern transport of ice-rafted debris as inferred from iceberg drift observations. The best sorted of those sandy end-members however also appears to be concentrated in regions characterized by high-energy turbidity and contour currents and so may also represent hydraulically winnowed sediment. The distribution of two lutite end-members appears in general to reflect the transport of fines by moderate to low energy thermohaline currents; although, in Baffin Bay and the northeastern North Atlantic the lutite could have accumulated primarily in turbidites. Ice-rafting by icebergs calved from Greenland glaciers, the reworking of glacigenic sediments on the Iceland—Faeroes Ridge and injection of turbid glacial meltwater into deep Baffin Bay from West Greenland fiords are suggested as the principal means of introduction of clastic particles into the sediment distribution (redistribution) budget of the deep North Atlantic.

Nutrient Regeneration in Deep Baffin Bay with Consequences for Measurements of the Conservative Tracer NO and Fossil Fuel CO2 in the Oceans

We found the nitrate to phosphate ratio of nutrients regenerated in Baffin Bay to be lower than is typical of most other ocean regions. The conservative tracers NO and PO are constant for water below 500 m providing NO and PO are redefined to account for this different nitrogen to phosphate ratio in the decaying organic matter of Baffin Bay. A modified stoichiometric model for decaying organic material in Baffin Bay was constructed based on measured values of carbonate, nitrate, and phosphate. A major difficulty in assessing the amount of fossil fuel CO2 in the ocean is the determination of the amount of inorganic carbon produced during the decay of biogenic material. Using the modified stoichiometric model for decaying biogenic material, we show how regional and seasonal variations in the amount of carbon released and oxygen consumed during decay could be sufficiently different from what is predicted by the Redfield–Ketchum–Richards model to cause major differences in the assessment of the amount of fossil fuel CO2 present in the water. The modified stoichiometric model offers the opportunity to determine the oxygen–carbon relationships more accurately and to obtain better estimates of fossil fuel CO2 in the ocean.

On the Origin of Deep Baffin Bay Water

A comparison of the temperature–salinity relationships of waters found in the Arctic Ocean, Baffin Bay and Smith Sound shows that the deep Baffin Bay water originates in the Arctic Ocean rather than through an influx of a mixture of Labrador Sea deep water and Baffin Bay surface water, the salinity of which has been increased sufficiently by freezing to cause the water to sink, as suggested previously by other investigators.