18 research outputs found
Global perspectives on observing ocean boundary current systems
© The Author(s), 2019. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Todd, R. E., Chavez, F. P., Clayton, S., Cravatte, S., Goes, M., Greco, M., Ling, X., Sprintall, J., Zilberman, N., V., Archer, M., Aristegui, J., Balmaseda, M., Bane, J. M., Baringer, M. O., Barth, J. A., Beal, L. M., Brandt, P., Calil, P. H. R., Campos, E., Centurioni, L. R., Chidichimo, M. P., Cirano, M., Cronin, M. F., Curchitser, E. N., Davis, R. E., Dengler, M., deYoung, B., Dong, S., Escribano, R., Fassbender, A. J., Fawcett, S. E., Feng, M., Goni, G. J., Gray, A. R., Gutierrez, D., Hebert, D., Hummels, R., Ito, S., Krug, M., Lacan, F., Laurindo, L., Lazar, A., Lee, C. M., Lengaigne, M., Levine, N. M., Middleton, J., Montes, I., Muglia, M., Nagai, T., Palevsky, H., I., Palter, J. B., Phillips, H. E., Piola, A., Plueddemann, A. J., Qiu, B., Rodrigues, R. R., Roughan, M., Rudnick, D. L., Rykaczewski, R. R., Saraceno, M., Seim, H., Sen Gupta, A., Shannon, L., Sloyan, B. M., Sutton, A. J., Thompson, L., van der Plas, A. K., Volkov, D., Wilkin, J., Zhang, D., & Zhang, L. Global perspectives on observing ocean boundary current systems. Frontiers in Marine Science, 6, (2010); 423, doi: 10.3389/fmars.2019.00423.Ocean boundary current systems are key components of the climate system, are home to highly productive ecosystems, and have numerous societal impacts. Establishment of a global network of boundary current observing systems is a critical part of ongoing development of the Global Ocean Observing System. The characteristics of boundary current systems are reviewed, focusing on scientific and societal motivations for sustained observing. Techniques currently used to observe boundary current systems are reviewed, followed by a census of the current state of boundary current observing systems globally. The next steps in the development of boundary current observing systems are considered, leading to several specific recommendations.RT was supported by The Andrew W. Mellon Foundation Endowed Fund for Innovative Research at WHOI. FC was supported by the David and Lucile Packard Foundation. MGo was funded by NSF and NOAA/AOML. XL was funded by Chinaâs National Key Research and Development Projects (2016YFA0601803), the National Natural Science Foundation of China (41490641, 41521091, and U1606402), and the Qingdao National Laboratory for Marine Science and Technology (2017ASKJ01). JS was supported by NOAAâs Global Ocean Monitoring and Observing Program (Award NA15OAR4320071). DZ was partially funded by the Joint Institute for the Study of the Atmosphere and Ocean (JISAO) under NOAA Cooperative Agreement NA15OAR4320063. BS was supported by IMOS and CSIROâs Decadal Climate Forecasting Project. We gratefully acknowledge the wide range of funding sources from many nations that have enabled the observations and analyses reviewed here
The influence of zooplankton and oxygen on the particulate organic carbon flux in the Benguela Upwelling System
We conducted extensive sediment trap experiments in the Benguela Upwelling System (BUS) in the south-eastern Atlantic Ocean to study the influence of zooplankton on the flux of particulate organic carbon (POC) through the water column and its sedimentation. Two long term moored and sixteen short term free-floating sediment trap systems were deployed. The mooring experiments were conducted for several years and the sixteen drifters were deployed on three different research cruises between 2019 and 2021. Zooplankton was separated from the trapped material and divided into 8 different zooplankton groups. In contrast to zooplankton which actively carries POC into the traps in the form of biomass (active POC flux), the remaining fraction of the trapped material was assumed to fall passively into the traps along with sinking particles (passive POC flux). The results show, in line with other studies, that copepods dominate the active POC flux, with the active POC flux in the southern BUS (sBUS) being about three times higher than in the northern BUS (nBUS). In contrast, the differences between the passive POC fluxes in the nBUS and sBUS were small. Despite large variations, which reflected the variability within the two subsystems, the mean passive POC fluxes from the drifters and the moored traps could be described using a common POC flux attenuation equation. However, the almost equal passive POC flux, on the one hand, and large variations in the POC concentration in the surface sediments between the nBUS and sBUS, on the other hand, imply that factors others than the POC supply exert the main control on POC sedimentation in the BUS. The varying intensity of the near-bottom oxygen minimum zone (OMZ), which is more pronounced in the nBUS than in the sBUS, could in turn explain the differences in the sediments, as the lack of oxygen reduces the POC degradation. Hence, globally expanding OMZs might favour POC sedimentation in regions formerly exposed to oxygenated bottom water but bear the risk of increasing the frequency of anoxic events in the oxygen-poor upwelling systems. Apart from associated release of CH4, which is a much more potent greenhouse gas than CO2, such events pose a major threat to the pelagic ecosystem and fisheries
Spatio-temporal variability of copepod abundance along the 20 °S monitoring transect in the Northern Benguela upwelling system from 2005 to 2011.
Long-term data sets are essential to understand climate-induced variability in marine ecosystems. This study provides the first comprehensive analysis of longer-term temporal and spatial variations in zooplankton abundance and copepod community structure in the northern Benguela upwelling system from 2005 to 2011. Samples were collected from the upper 200 m along a transect at 20 °S perpendicular to the coast of Namibia to 70 nm offshore. Based on seasonal and interannual trends in surface temperature and salinity, three distinct time periods were discernible with stronger upwelling in spring and extensive warm-water intrusions in late summer, thus, high temperature amplitudes, in the years 2005/06 and 2010/11, and less intensive upwelling followed by weaker warm-water intrusions from 2008/09 to 2009/10. Zooplankton abundance reflected these changes with higher numbers in 2005/06 and 2010/11. In contrast, zooplankton density was lower in 2008/09 and 2009/10, when temperature gradients from spring to late summer were less pronounced. Spatially, copepod abundance tended to be highest between 30 and 60 nautical miles off the coast, coinciding with the shelf break and continental slope. The dominant larger calanoid copepods were Calanoides carinatus, Metridia lucens and Nannocalanus minor. On all three scales studied, i.e. spatially from the coast to offshore waters as well as temporally, both seasonally and interannually, maximum zooplankton abundance was not coupled to the coldest temperature regime, and hence strongest upwelling intensity. Pronounced temperature amplitudes, and therefore strong gradients within a year, were apparently important and resulted in higher zooplankton abundance
Spatial and biomass structure of shallow-water cape hake (Merluccius capensis) in the light of episodic environmental shifts
The spatial distribution patterns of Merluccius capensis in the Namibian waters were
investigated and related to average environmental conditions during 1996â2020.
Fisheries-independent data and simultaneously collected water temperature and dis-
solved oxygen data were used from austral summer surveys. A geostatistical kriging
approach was employed to evaluate the spatial structure of hakes. Links to environ-
mental conditions were explored via data-driven generalized additive models
(GAMs). M. capensis generally exhibited average patch sizes between 40 and 50 nm
at depths between 180 and 280 m. During the extreme episodic water warming in
2011 related to a Benguela-Niño, the hake patches shrank up to a historical minimum
of about 13 nm and moved offshore showing maximum densities at unusual deeper
bottoms between 260 and 320 m. The deepening and size reduction of aggregations
did not alter the biomass estimates (570 kt) that remained within historical ranges
(249â811 kt). Although other extremely warm and cold summers were reported dur-
ing the study period, no significant impact on the M. capensis patch size was
detected. Maximum M. capensis densities were linked to optimal bottom temperature
range between 10.1 and 11.8C, dissolved oxygen values close to zero nearshore,
and between 0.8 and 1.4 ml/L offshore. Potential changes of biomass produced by
extreme environmental events remained undetected within the interannual biomass
ranges, suggesting a high resilience capacity to episodic extreme environmental
events.Peer reviewe
Regional and global impact of CO2 uptake in the Benguela Upwelling System through preformed nutrients
Abstract Eastern Boundary Upwelling Systems (EBUS) are highly productive ecosystems. However, being poorly sampled and represented in global models, their role as atmospheric CO2 sources and sinks remains elusive. In this work, we present a compilation of shipboard measurements over the past two decades from the Benguela Upwelling System (BUS) in the southeast Atlantic Ocean. Here, the warming effect of upwelled waters increases CO2 partial pressure (pCO2) and outgassing in the entire system, but is exceeded in the south through biologically-mediated CO2 uptake through biologically unused, so-called preformed nutrients supplied from the Southern Ocean. Vice versa, inefficient nutrient utilization leads to preformed nutrient formation, increasing pCO2 and counteracting human-induced CO2 invasion in the Southern Ocean. However, preformed nutrient utilization in the BUS compensates with ~22â75 Tg C yearâ1 for 20â68% of estimated natural CO2 outgassing in the Southern Oceanâs Atlantic sector (~ 110 Tg C yearâ1), implying the need to better resolve global change impacts on the BUS to understand the oceanâs role as future sink for anthropogenic CO2
Log-transformed monthly anomalies between 2005 and 2011 of a) temperature at 10 m, b) chlorophyll <i>a</i>, and abundance (no. m<sup>â2</sup>) of c) total zooplankton, d) total copepods, e) <i>Calanoides carinatus</i>, f) <i>Metridia lucens</i>, and g) <i>Nannocalanus minor</i>.
<p>Log-transformed monthly anomalies between 2005 and 2011 of a) temperature at 10 m, b) chlorophyll <i>a</i>, and abundance (no. m<sup>â2</sup>) of c) total zooplankton, d) total copepods, e) <i>Calanoides carinatus</i>, f) <i>Metridia lucens</i>, and g) <i>Nannocalanus minor</i>.</p
Location of the monitoring transect at 20°S off Namibia and approximate position of the Angola Benguela Front (ABF).
<p>Location of the monitoring transect at 20°S off Namibia and approximate position of the Angola Benguela Front (ABF).</p
Abundances (no. m<sup>â2</sup>) of <i>Calanoides carinatus</i> in relation to chlorophyll <i>a</i> concentration and temperature at 10 m depth.
<p>The area of each circle is proportional to the abundance shown in the legend.</p
Inshore (triangles), shelf (circles) and offshore (squares) stations arranged according to the first two principal components.
<p>For a better overview, upwelling months (June-November) are black, while quiescent months (February to April) are light grey. Data of May and December are marked in dark grey, since these months showed a distinct oceanographic regime compared to the other months (start and end of upwelling period).</p
Mean annual abundance (no. m<sup>â2</sup>Ă10<sup>3</sup>±SD) of a) total zooplankton, total copepods, cyclopoid and calanoid copepods and the dominant species b) <i>Calanoides carinatus</i>, <i>Metridia lucens</i> and <i>Nannocalanus minor</i> for each year recorded.
<p>Mean annual abundance (no. m<sup>â2</sup>Ă10<sup>3</sup>±SD) of a) total zooplankton, total copepods, cyclopoid and calanoid copepods and the dominant species b) <i>Calanoides carinatus</i>, <i>Metridia lucens</i> and <i>Nannocalanus minor</i> for each year recorded.</p