Stable isotope ratios in seawater nitrate reflect the influence of Pacific water along the northwest Atlantic margin

Sherwood, Owen A.; Davin, Samuel H.; Lehmann, Nadine; Buchwald, Carolyn; Edinger, Evan; Lehmann, Moritz F.; Kienast, Markus

doi:10.5194/bg-18-4491-2021

Cited by 12 publications

(12 citation statements)

References 103 publications

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“…Similarly, high POM d 15 N values for Stations 224 and 193 in the BIC are likely influenced by the Pacific d 15 NO 3 propagating south from Lancaster Sound. This interpretation would be consistent with recent work showing the Pacific d 15 NO 3 signature is not only entrained into the BIC, but subsequently carried into the Labrador Current (Sherwood et al, 2021).…”

Section: Sources Of Particulate Organic Carbon and Nitrogen In Baffin...supporting

confidence: 92%

“…These stations similarly cluster together in d 13 C-d 15 N space, with an average d 15 N = 4.1 ± 0.3‰ (n = 3; Figure 3B). Thus, we conclude that for most WGC stations, POM d 13 C and d 15 N values can be attributed to the prevalence of high-latitude phytoplankton utilizing the inflow of WGC and Irminger Current water as their main d 15 NO 3 source (+4-6‰; Sherwood et al, 2021). Station 204 has negative POM d 13 C (−27.8‰) and positive d 13 N(+5.1‰) values, but falls on a continuum between Atlantic WGC water to Central Baffin Bay isotopic endmembers (Figure 3B).…”

Section: Sources Of Particulate Organic Carbon and Nitrogen In Baffin...mentioning

confidence: 82%

“…For example, nitrate d 15 N (d 15 NO 3 ) in the surface ocean has a large range (+2 to +20‰; Rafter et al, 2019), and is largely determined by nutrient availability and biological processes fractionating the surface nitrate pool (e.g., assimilation vs. denitrification and remineralization). Probable d 15 NO 3 signatures that can be incorporated into surface POM d 15 N in Baffin Bay include nitrate from: the Atlantic Ocean (+4 to +6‰; Sherwood et al, 2021), the Pacific Ocean via the CAA (+7 to +8‰; Brown et al, 2015;Granger et al, 2018), and the Arctic Ocean (+5 to +7‰; Fripiat et al, 2018;Rafter et al, 2019).…”

Section: Introductionmentioning

confidence: 99%

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Sources and Cycling of Particulate Organic Matter in Baffin Bay: A Multi-Isotope δ13C, δ15N, and Δ14C Approach

Fox

Walker

2022

Front. Mar. Sci.

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The Canadian Arctic is warming three times faster than the rest of the planet. The impact of climate change on the Arctic carbon cycle, and in particular for Baffin Bay, remains poorly constrained. Sinking particulate organic matter (POMsink) is a key component of the biological carbon pump and provides a direct linkage between surface productivity and the preservation of carbon in marine sediments. While POMsink provides a rapid POM shunt to the deep ocean (days) the majority of marine POM is suspended (POMsusp) persists for years in the water column. Stable carbon (δ13C), nitrogen (δ15N) and radiocarbon (Δ14C) measurements are powerful tools for evaluating sources and cycling of POM. In this study, we measure depth-integrated (0-400m) POMsusp stable carbon (δ13C), nitrogen (δ15N) and radiocarbon (Δ14C) values at 11 stations in Baffin Bay. We use POM C:Na ratios to evaluate its diagenetic state. POMsusp δ13C and δ15N values ranged from −21.6‰ to −29.5‰, and +3.84‰ to +7.21‰, respectively. POMsusp Δ14C values ranged from −41.8‰ to +76.8‰. Together, our results suggest Baffin Bay POMsusp has multiple carbon and nitrogen sources. POMsusp δ13C and Δ14C are strongly correlated to surface salinity, indicating surface water has a strong influence on POMsusp isotopic composition and 14C-age. POMsusp from coastal Greenland stations have similar Δ14C values to surface dissolved inorganic carbon (DIC) and POM concentrations, consistent with primary production as the predominant POMsusp source in Eastern Baffin Bay. Positive POMsusp Δ14C values in central Baffin Bay suggest an accumulation of atmospheric “bomb” 14C in the sub-polar gyre. POMsusp exiting Davis Strait via the Baffin Island Current was determined to have a significant degraded, resuspended sediment component. Finally, POMsusp δ15N values highlight two distinct N sources in Baffin Bay: Pacific and Arctic nutrients at Northern gateway stations vs. the influx of Atlantic nutrients via Davis Strait along coastal Greenland. Overall, these first Baffin Bay POMsusp Δ14C values provide useful baseline data for rapidly changing Arctic ecosystem.

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Section: Sources Of Particulate Organic Carbon and Nitrogen In Baffin...supporting

confidence: 92%

Section: Sources Of Particulate Organic Carbon and Nitrogen In Baffin...mentioning

confidence: 82%

Section: Introductionmentioning

confidence: 99%

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Sources and Cycling of Particulate Organic Matter in Baffin Bay: A Multi-Isotope δ13C, δ15N, and Δ14C Approach

Fox

Walker

2022

Front. Mar. Sci.

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“…The progressive dilution of the Pacific signal within the BIC reflects the recirculation and mixing of the Arctic outflows through Nares Strait, Jones Sound, Lancaster Sound, and the WGC as part of the general cyclonic circulation in Baffin Bay (Figures 1 and 2; Azetsu‐Scott et al., 2012; Lehmann et al., 2019). While tracer distributions show little influence of Pacific‐derived nutrients in the central Labrador Sea (LS2), a detectable Pacific signal is traced along the western North Atlantic margin (Jones, 2003; Sherwood et al., 2021).…”

Section: Discussionmentioning

confidence: 99%

Physical and Biogeochemical Influences on Nutrients Through the Canadian Arctic Archipelago: Insights From Nitrate Isotope Ratios

et al. 2022

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The Canadian Arctic Archipelago (CAA) provides a gateway for the flow of nutrients from the North Pacific to the North Atlantic. The transport and biogeochemical cycling of nutrients throughout the CAA, however, are sparsely documented. Here, we report water column nitrogen and oxygen isotope ratios of nitrate (δ15NNO3 and δ18ONO3) collected in a throughflow of the CAA into Baffin Bay, providing insights on inherent nutrient dynamics. The nitracline shoaled eastward into the CAA, wherein large subsurface chlorophyll maxima and coincident increases in δ15NNO3 and δ18ONO3 indicated enhanced nitrate assimilation relative to the oligotrophic Canada Basin. High δ15NNO3 values characteristic of Pacific Winter Water (PWW) pervaded the Archipelago and Baffin Bay, decreasing eastward due to mixing with underlying Atlantic water (AW)—from the Canada Basin west of Barrow Strait, and from Baffin Bay east thereof. Nearly 25% of nutrients in the central CAA were of Atlantic origin, a substantially larger fraction than surmised previously. Nutrient properties in the CAA were notably not influenced by benthic denitrification. Those in underlying AW in the western CAA, however, were modified by remineralization of Pacific‐sourced nutrients, manifested from increases in δ15NNO3 relative to the Canada Basin. Properties in the eastern CAA exposed the complex hydrography of Baffin Bay, characterized by lateral intrusions of nutrient‐poor winter waters into PWW and of cold mode waters in underlying AW. High δ15NNO3 values in AW revealed the presence of a substantial fraction of N from remineralization, stemming from the high productivity in Baffin Bay fueled by Pacific nutrients.

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“…Potential temperature (θ) and density of seawater at atmospheric pressure (σθ) were calculated based on water temperature, pressure and salinity measured on the ship (SBE 9plus CTD, Seabird Scientific, Canada) (Amundsen Science Data Collection, 2021d) using the package 'seawater' in Python (calculations based on Bryden, 1973;Fofonoff and Millard, 1983;Millero and Poisson, 1981). Water masses were assigned according to operational definitions considering specified ranges of calculated potential temperature and density of seawater (Table 1 in Sherwood et al, 2021;Stramma et al, 2004;Fratantoni and Pickart, 2007;Azetsu-Scott et al, 2012)…”

Section: Water Column Measurementsmentioning

confidence: 99%

Methane flux estimates from continuous atmospheric measurements and surface-water observations in the northern Labrador Sea and Baffin Bay

Vogt

Risk

Azetsu-Scott

et al. 2022

Preprint

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Abstract. Vast amounts of methane (CH4) stored in permafrost and submarine sediments are susceptible to release in a warming Arctic, further exacerbating climate change in a positive feedback. It is therefore critical to monitor CH4 over pan-regional scales to detect early signs of CH4 release. However, our ability to monitor CH4 is hampered in remote northern regions by sampling and logistical constraints and few good baseline data exist in many areas. To create a baseline study of current background levels of CH4 in North Atlantic waters, we collected continuous real-time atmospheric CH4 data, along with ambient air temperature and wind parameters over 22 days in summer 2021 on a roughly 5100 km voyage in the northern Labrador Sea and Baffin Bay up to 71° N. In addition, we measured CH4 concentrations in the water column using discrete water samples at selected stations. Measured atmospheric mixing ratios of CH4 ranged from 1944.7 ppb to 2012.0 ppb, with a mean of 1966.0±7.4 ppb and a baseline of 1954.2−1980.6 ppb. Dissolved CH4 concentrations in the near-surface water peaked at 56.58±0.05 nM within 1 km down-current of a known cold seep at Scott Inlet but were consistently super-saturated throughout the water column in Southwind Fjord, which is an area recently affected by submarine landslides. Local sea-air CH4 fluxes ranged from 0.1−14.1 µmol m-2 d-1 indicating that the ocean acted as a CH4 source to the atmosphere. Atmospheric CH4 levels were also driven by meteorological, spatial, and temporal variations. Highest atmospheric CH4 mixing ratios were detected in the Cumberland Sound in Nunavut, suggesting onshore sources from nearby waterbodies and wetlands, whereas ocean-based contributions at this location could not be ruled out. Coupled real-time measurements of marine and atmospheric CH4 data have the potential to provide ongoing monitoring in a region susceptible to CH4 releases, as well as critical validation data for global-scale measurements and modelling.

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Stable isotope ratios in seawater nitrate reflect the influence of Pacific water along the northwest Atlantic margin

Cited by 12 publications

References 103 publications

Sources and Cycling of Particulate Organic Matter in Baffin Bay: A Multi-Isotope δ13C, δ15N, and Δ14C Approach

Sources and Cycling of Particulate Organic Matter in Baffin Bay: A Multi-Isotope δ13C, δ15N, and Δ14C Approach

Physical and Biogeochemical Influences on Nutrients Through the Canadian Arctic Archipelago: Insights From Nitrate Isotope Ratios

Methane flux estimates from continuous atmospheric measurements and surface-water observations in the northern Labrador Sea and Baffin Bay

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