scholarly journals Timing of nutrient depletion, diatom dominance and a lower-boundary estimate of export production for Irminger Basin, North Atlantic

2006 ◽  
Vol 313 ◽  
pp. 73-84 ◽  
Author(s):  
SA Henson ◽  
R Sanders ◽  
C Holeton ◽  
JT Allen
Keyword(s):  
North Atlantic ◽  
Lower Boundary ◽  
Nutrient Depletion ◽  
Boundary Estimate ◽  
Export Production

scholarly journals Amazon River influence on nitrogen fixation and export production in the western tropical North Atlantic

2016 ◽  
Vol 62 (2) ◽  
pp. 618-631 ◽  
Author(s):  
Sarah C. Weber ◽  
Edward J. Carpenter ◽  
Victoria J. Coles ◽  
Patricia L. Yager ◽  
Joaquim Goes ◽  
...  
Keyword(s):  
Nitrogen Fixation ◽  
North Atlantic ◽  
Amazon River ◽  
Export Production ◽  
Tropical North Atlantic

scholarly journals Oxygen Utilization and Downward Carbon Flux in an Oxygen-Depleted Eddy in the Eastern Tropical North Atlantic

2016 ◽  
Author(s):  
B. Fiedler ◽  
D. Grundle ◽  
F. Schütte ◽  
J. Karstensen ◽  
C. R. Löscher ◽  
...  
Keyword(s):  
Organic Matter ◽  
North Atlantic ◽  
Lower Boundary ◽  
Euphotic Zone ◽  
Shallow Depth ◽  
Surface Mixed Layer ◽  
Low Oxygen ◽  
Oxygen Utilization ◽  
Near Surface ◽  
Tropical North Atlantic

Abstract. The occurrence of mesoscale eddies that develop an extreme low oxygen environment at shallow depth (about 40 to 100 m) has recently been reported for the eastern tropical North Atlantic (ETNA). Their hydrographic structure suggests that the water mass inside the eddy is well isolated from ambient waters supporting the development of severe near-surface oxygen deficits. So far, hydrographic and biogeochemical characterization of these eddies was limited to a few autonomous surveys, using moorings, underwater gliders and profiling floats. In this study we present results from the first dedicated biogeochemical survey of one of these eddies conducted in March 2014 near the Cape Verde Ocean Observatory (CVOO). At the time of the survey the eddy core showed lowest oxygen concentrations of less than 5 μmol kg−1 and a pH of approx. 7.6 at the lower boundary of the euphotic zone. Correspondingly, the aragonite saturation level dropped to 1 thereby creating unfavorable conditions for calcifying organisms at this shallow depth. To our knowledge, such enhanced acidity within near-surface waters has never been reported before for the open Atlantic Ocean. Vertical distributions of particulate and dissolved organic matter (POM, DOM) generally show elevated concentrations in the surface mixed layer, but particularly DOM also accumulates beneath the oxygen minimum. Considering reference data from the upwelling region where these eddies are formed, we determined the oxygen consumption through remineralization of organic matter and found an enhancement of apparent oxygen utilization rates (aOUR, 0.26 μmol kg−1 d−1) by almost one order of magnitude when compared with typical values for the open North Atlantic. Computed downward fluxes for particulate organic carbon (POC) at 100 m were about 0.19 to 0.23 g C m−2 d−1 which clearly exceed fluxes typical for an oligotrophic open ocean setting. The observations support the view that the oxygen depleted eddies can be viewed as isolated, westwards propagating upwelling systems as their own.

On the Assessment of Nonlocal Climate Feedback. Part II: EFA-SVD and Optimal Feedback Modes*

2008 ◽  
Vol 21 (20) ◽  
pp. 5402-5416 ◽  
Author(s):  
Zhengyu Liu ◽  
Na Wen
Keyword(s):  
Heat Flux ◽  
North Atlantic ◽  
Upper Bound ◽  
Geopotential Height ◽  
Large Scale ◽  
Lower Boundary ◽  
Climate Feedback ◽  
Optimal Feedback ◽  
Basin Scale ◽  
Ocean Atmosphere

Abstract The equilibrium feedback assessment (EFA) is combined with the singular value decomposition (SVD) to assess the large-scale feedback modes from a lower boundary variability field onto an atmospheric field. The leading EFA-SVD modes are the optimal feedback modes, with the lower boundary forcing patterns corresponding to those that generate the largest atmospheric responses, and therefore provide upper bounds of the feedback response. The application of EFA-SVD to an idealized coupled ocean–atmosphere model demonstrates that EFA-SVD is able to extract the leading feedback modes successfully. Furthermore, these large-scale modes are the least sensitive to sampling errors among all the feedback processes and therefore are the most robust for statistical estimation. The EFA-SVD is then applied to the observed North Atlantic ocean–atmosphere system for the assessment of the sea surface temperature (SST) feedback on the surface heat flux and the geopotential height, respectively. The dominant local negative feedback of SST on heat flux is confirmed, with an upper bound of about 40 W m−2 K−1 for basin-scale anomalies. The SST also seems to exert a strong feedback on the atmospheric geopotential height: the optimal SST forcing has a dipole pattern that generates an optimal response of a North Atlantic Oscillation (NAO) pattern, with an upper bound of about 70 m K−1 at 500 hPa. Further issues on the EFA-SVD analysis are also discussed.

scholarly journals Estimating the convective supply of nitrate and implied variability in export production over the North Atlantic

2000 ◽  
Vol 14 (4) ◽  
pp. 1299-1313 ◽  
Author(s):  
Richard G. Williams ◽  
Alison J. McLaren ◽  
Michael J. Follows
Keyword(s):  
North Atlantic ◽  
Export Production ◽  
The North ◽  
The North Atlantic

scholarly journals Distribution and rates of nitrogen fixation in the western tropical South Pacific Ocean constrained by nitrogen isotope budgets

2018 ◽  
Vol 15 (9) ◽  
pp. 2619-2628 ◽  
Author(s):  
Angela N. Knapp ◽  
Kelly M. McCabe ◽  
Olivier Grosso ◽  
Nathalie Leblond ◽  
Thierry Moutin ◽  
...  
Keyword(s):  
Spatial Distribution ◽  
North Atlantic ◽  
N2 Fixation ◽  
South Pacific ◽  
Nitrogen Isotope ◽  
Eastern Tropical Pacific ◽  
Export Production ◽  
South Pacific Ocean ◽  
N Removal ◽  
Tropical North Atlantic

Abstract. Constraining the rates and spatial distribution of dinitrogen (N2) fixation fluxes to the ocean informs our understanding of the environmental sensitivities of N2 fixation as well as the timescale over which the fluxes of nitrogen (N) to and from the ocean may respond to each other. Here we quantify rates of N2 fixation as well as its contribution to export production along a zonal transect in the western tropical South Pacific (WTSP) Ocean using N isotope (“δ15N”) budgets. Comparing measurements of water column nitrate + nitrite δ15N with the δ15N of sinking particulate N at a western, central, and eastern station, these δ15N budgets indicate high, modest, and low rates of N2 fixation at the respective stations. The results also imply that N2 fixation supports exceptionally high, i.e. ≥ 50 %, of export production at the western and central stations, which are also proximal to the largest iron sources. These geochemically based rates of N2 fixation are equal to or greater than those previously reported in the tropical North Atlantic, indicating that the WTSP Ocean has the capacity to support globally significant rates of N2 fixation, which may compensate for N removal in the oxygen-deficient zones of the eastern tropical Pacific.

Stratosphere–Troposphere Coupling during Spring Onset

2006 ◽  
Vol 19 (19) ◽  
pp. 4891-4901 ◽  
Author(s):  
Robert X. Black ◽  
Brent A. McDaniel ◽  
Walter A. Robinson
Keyword(s):  
North Atlantic ◽  
High Latitude ◽  
Seasonal Cycle ◽  
Large Scale ◽  
Vortex Breakdown ◽  
Lower Boundary ◽  
Polar Vortex ◽  
Stratospheric Polar Vortex ◽  
Near Surface ◽  
Circulation Anomalies

Abstract The authors perform an observational study of the relation between stratospheric final warmings (SFWs) and the boreal extratropical circulation. SFW events are found to provide a strong organizing influence upon the large-scale circulation of the stratosphere and troposphere during the period of spring onset. In contrast to the climatological seasonal cycle, SFW events noticeably sharpen the annual weakening of high-latitude circumpolar westerlies in both the stratosphere and troposphere. A coherent pattern of significant westerly (easterly) zonal wind anomalies is observed to extend from the stratosphere to the earth’s surface at high latitudes prior to (after) SFW events, coinciding with the polar vortex breakdown. This evolution is associated with a bidirectional dynamical coupling of the stratosphere–troposphere system in which tropospheric low-frequency waves induce annular stratospheric circulation anomalies, which in turn, are followed by annular tropospheric circulation anomalies. The regional tropospheric manifestation of SFW events consists of a North Atlantic Oscillation (NAO)-like phase transition in the near-surface geopotential height field, with height rises over polar latitudes and height falls over the northeast North Atlantic. This lower-tropospheric change pattern is distinct from the climatological seasonal cycle, which closely follows seasonal trends in thermal forcing at the lower boundary. Although broadly similar, the tropospheric anomaly patterns identified in the study do not precisely correspond to the canonical northern annular mode (NAM) and NAO patterns as the primary anomaly centers are retracted northward toward the pole. The results here imply that (i) high-latitude climate may be particularly sensitive to long-term trends in the annual cycle of the stratospheric polar vortex and (ii) improvements in the understanding and simulation of SFW events may benefit medium-range forecasts of spring onset in the extratropics.

scholarly journals An estimate of the terrestrial carbon budget of Russia using inventory-based, eddy covariance and inversion methods

2012 ◽  
Vol 9 (12) ◽  
pp. 5323-5340 ◽  
Author(s):  
A. J. Dolman ◽  
A. Shvidenko ◽  
D. Schepaschenko ◽  
P. Ciais ◽  
N. Tchebakova ◽  
...  
Keyword(s):  
Eddy Covariance ◽  
Lower Boundary ◽  
Boundary Estimate ◽  
Eddy Covariance Method ◽  
Forest Inventories ◽  
Inversion Methods ◽  
Inverse Models ◽  
Vegetation Models ◽  
Global Vegetation ◽  
And Inversion

Abstract. We determine the net land to atmosphere flux of carbon in Russia, including Ukraine, Belarus and Kazakhstan, using inventory-based, eddy covariance, and inversion methods. Our high boundary estimate is −342 Tg C yr−1 from the eddy covariance method, and this is close to the upper bounds of the inventory-based Land Ecosystem Assessment and inverse models estimates. A lower boundary estimate is provided at −1350 Tg C yr−1 from the inversion models. The average of the three methods is −613.5 Tg C yr−1. The methane emission is estimated separately at 41.4 Tg C yr−1. These three methods agree well within their respective error bounds. There is thus good consistency between bottom-up and top-down methods. The forests of Russia primarily cause the net atmosphere to land flux (−692 Tg C yr−1 from the LEA. It remains however remarkable that the three methods provide such close estimates (−615, −662, −554 Tg C yr–1) for net biome production (NBP), given the inherent uncertainties in all of the approaches. The lack of recent forest inventories, the few eddy covariance sites and associated uncertainty with upscaling and undersampling of concentrations for the inversions are among the prime causes of the uncertainty. The dynamic global vegetation models (DGVMs) suggest a much lower uptake at −91 Tg C yr−1, and we argue that this is caused by a high estimate of heterotrophic respiration compared to other methods.

scholarly journals Distribution and rates of nitrogen fixation in the western tropical South Pacific Ocean constrained by nitrogen isotope budgets

2018 ◽  
Author(s):  
Angela N. Knapp ◽  
Kelly M. McCabe ◽  
Olivier Grosso ◽  
Nathalie Leblond ◽  
Thierry Moutin ◽  
...  
Keyword(s):  
Spatial Distribution ◽  
North Atlantic ◽  
N2 Fixation ◽  
South Pacific ◽  
Nitrogen Isotope ◽  
Eastern Tropical Pacific ◽  
Export Production ◽  
South Pacific Ocean ◽  
N Removal ◽  
Tropical North Atlantic

Abstract. Constraining the rates and spatial distribution of di-nitrogen (N2) fixation fluxes to the ocean informs our understanding of the environmental sensitivities of N2 fixation as well as the timescale over which the fluxes of nitrogen (N) to and from the ocean may respond to each other. Here we quantify rates of N2 fixation as well as its contribution to export production along a zonal transect in the Western Tropical South Pacific (WTSP) Ocean using N isotope (δ15N) budgets. Comparing measurements of water column nitrate + nitrite δ15N with the δ15N of sinking particulate N at a western, central, and eastern station, these δ15N budgets indicate high, modest, and low rates of N2 fixation at the respective stations. The results also imply that N2 fixation supports exceptionally high, i.e., > 50 %, of export production at the western and central stations, which are also proximal to the largest iron sources. These geochemically-based rates of N2 fixation are equal to or greater than those previously reported in the tropical North Atlantic, indicating that the WTSP Ocean has the capacity to support globally significant rates of N2 fixation, which may compensate for N removal in the oxygen deficient zones of the eastern tropical Pacific.

The Atmospheric Response to North Atlantic SST Trends, 1870–2019

2020 ◽  
Author(s):  
Kristopher B. Karnauskas ◽  
Lei Zhang ◽  
Dillon J. Amaya
Keyword(s):  
North Atlantic ◽  
Atmospheric Response
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