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 China’s 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 NOAA’s 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 CSIRO’s 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

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 1996–2020. 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 (249–811 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 ~22–75 Tg C year−1 for 20–68% of estimated natural CO2 outgassing in the Southern Ocean’s Atlantic sector (~ 110 Tg C year−1), implying the need to better resolve global change impacts on the BUS to understand the ocean’s role as future sink for anthropogenic CO2

Abundances (no. m⁻²) 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

Log-transformed monthly anomalies between 2005 and 2011 of a) temperature at 10 m, b) chlorophyll <i>a</i>, and abundance (no. m⁻²) 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⁻²) 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

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⁻²×10³±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⁻²×10³±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

Monthly means (±SD) of a) temperature at 10 m, b) chlorophyll <i>a</i>, c) total zooplankton, d) total copepods, e) calanoid copepods, f) <i>Calanoides carinatus</i>, g) <i>Metridia lucens</i> and h) <i>Nannocalanus minor</i>. Note different scales.

<p>Monthly means (±SD) of a) temperature at 10 m, b) chlorophyll <i>a</i>, c) total zooplankton, d) total copepods, e) calanoid copepods, f) <i>Calanoides carinatus</i>, g) <i>Metridia lucens</i> and h) <i>Nannocalanus minor</i>. Note different scales.</p