Uncovering the Composition and Diversity of Pelagic Copepods in the Oligotrophic Blue Water of the South Pacific Subtropical Gyre

The subtropical gyres occupy approximately 40% of the surface of the Earth and are widely recognized as oligotrophic zones. Among them, the South Pacific subtropical gyre (SPSG) shows the lowest chlorophyll-a levels (0.02–0.04 μgL–1), the deepest nutricline (>200 m) and euphotic zone (∼160 m), and the lowest rates of nitrogen fixation. The zooplankton community is poorly known in the SPSG. We report a study focused on the composition and distribution of pelagic copepods within the gyre so as to uncover the diversity and habitat conditions of this special community. Therefore, during the austral spring of 2015, an oceanographic cruise was conducted across the eastern side of the SPSG. Physical and chemical variables were measured in the upper 1000 m, while zooplankton samples were collected by means of vertically stratified hauls using a multiple net sampler for five layers (0–800 m). Satellite data were also used to assess near-surface phytoplankton biomass (Chl-a) and physical-dynamics conditions during the cruise, and 121 species of copepods were identified, which belonged to five taxonomic orders, 24 families, and 50 genera. Calanoida and Cyclopoida were the most frequent orders, containing 57% and 38% of species, respectively, whereas Harpacticoida and Mormonilloida contained 2% of species each, and Siphonostomatoida contained 1% of species. The vertical distribution of copepods revealed an ecological zonation linked to a strongly stratified water column, such that three different vertical habitats were defined: shallow (0–200 m), intermediate (200–400 m), and deep (400–800 m). Both the abundance and diversity of copepods were greater in the shallow habitat and were strongly associated with water temperature, whereas copepods in the subsurface layers subsisted with relatively low oxygen waters (2–3 mL O2 L–1) and presumably originated at the Chilean upwelling zone, being transported offshore by mesoscale eddies. Furthermore, the analysis of species composition revealed a marked dominance of small-sized copepods, which may play a key role in nutrient recycling under an oligotrophic condition, as inferred from their mostly omnivorous feeding behavior. Our findings also suggested a potentially high endemism within the gyre, although basin-scale circulation and mesoscale eddies, traveling from the coastal upwelling zone and transporting plankton, can also influence the epipelagic fauna.

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Seasonal Reversal of the Near‐Surface Chlorophyll Response to the Presence of Mesoscale Eddies in the South Pacific Subtropical Countercurrent

Journal of Geophysical Research Oceans ◽

10.1029/2019jc015752 ◽

2020 ◽

Vol 125 (3) ◽

Author(s):

Seth Travis ◽

Bo Qiu

Keyword(s):

Mesoscale Eddies ◽

South Pacific ◽

The South ◽

Near Surface ◽

Subtropical Countercurrent

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Circulation Regimes and Low-Frequency Oscillations in the South Pacific Sector

Monthly Weather Review ◽

10.1175//2548.1 ◽

2003 ◽

Vol 131 (8) ◽

pp. 1566-1576 ◽

Cited By ~ 31

Author(s):

Andrew W. Robertson ◽

Carlos R. Mechoso

Keyword(s):

Singular Spectrum Analysis ◽

Low Frequency ◽

South Pacific ◽

Stationary Wave ◽

Gaussian Mixture ◽

Reanalysis Data ◽

Oscillatory Behavior ◽

South American ◽

The South ◽

Austral Spring

Abstract The characteristics of subseasonal circulation variability over the South Pacific are examined using 10-day lowpass-filtered 700-hPa geopotential height NCEP–NCAR reanalysis data. The extent to which the variability in each season is characterized by recurrent geographically fixed circulation regimes and/or oscillatory behavior is determined. Two methods of analysis (a K-means cluster analysis and a cross-validated Gaussian mixture model) both indicate three to four geographically fixed circulation regimes in austral fall, winter, and (to some extent) spring. The spatial regime structures are found to be quite similar in each season; they resemble the so-called Pacific–South American (PSA) patterns discussed in previous studies and often referred to as PSA 1 and PSA 2. Oscillatory behavior is investigated using singular spectrum analysis. This identifies a predominantly stationary wave with a period of about 40 days and a spatial structure similar to PSA 1; it is most pronounced in winter and spring and exhibits a noticeable eastward drift as it decays. The power spectrum of variability is otherwise well approximated by a red spectrum, together with enhanced broader-band 15–30-day variability. The results presented herein indicate that low-frequency variability over the South Pacific is not dominated by a propagating wave whose quadrature phases are PSA 1 and PSA 2, as hitherto described. Rather, it is found that the variability is well described by the occurrence of three to four geographically fixed circulation regimes, with a (near) 40-day oscillation that is predominantly stationary in space. The potential subseasonal predictability implied by this duality is discussed. Only during austral spring is a strong correlation found between El Niño and the frequency of occurrence of the circulation regimes.

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Remote Sensing of Coastal Upwelling in the South-Eastern Baltic Sea: Statistical Properties and Implications for the Coastal Environment

Remote Sensing ◽

10.3390/rs10111752 ◽

2018 ◽

Vol 10 (11) ◽

pp. 1752 ◽

Cited By ~ 11

Author(s):

Toma Dabuleviciene ◽

Igor E. Kozlov ◽

Diana Vaiciute ◽

Inga Dailidiene

Keyword(s):

Baltic Sea ◽

Satellite Data ◽

Coastal Upwelling ◽

Optical Data ◽

Curonian Lagoon ◽

The South ◽

Near Surface ◽

South Eastern ◽

The Baltic ◽

Eastern Baltic

A detailed study of wind-induced coastal upwelling (CU) in the south-eastern Baltic Sea is presented based on an analysis of multi-mission satellite data. Analysis of moderate resolution imaging spectroradiometer (MODIS) sea surface temperature (SST) maps acquired between April and September of 2000–2015 allowed for the identification of 69 CU events. The Ekman-based upwelling index (UI) was applied to evaluate the effectiveness of the satellite measurements for upwelling detection. It was found that satellite data enable the identification of 87% of UI-based upwelling events during May–August, hence, serving as an effective tool for CU detection in the Baltic Sea under relatively cloud-free summer conditions. It was also shown that upwelling-induced SST drops, and its spatial properties are larger than previously registered. During extreme upwelling events, an SST drop might reach 14 °C, covering a total area of nearly 16,000 km2. The evolution of an upwelling front during such intensive events is accompanied by the generation of transverse filaments extending up to 70 km offshore. An analysis of the satellite optical data shows a clear decline in the chlorophyll-a concentration in the coastal zone and in the shallow Curonian Lagoon, where it drops down by an order of magnitude. It was also shown that a cold upwelling front alters the stratification in the atmospheric boundary layer, leading to a sudden drop of air temperature and near-surface winds.

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Seasonal to interannual variability from expendable bathythermograph and TOPEX/Poseidon altimeter data in the South Pacific subtropical gyre

Journal of Geophysical Research Atmospheres ◽

10.1029/2000jc900056 ◽

2000 ◽

Vol 105 (C8) ◽

pp. 19535-19550 ◽

Cited By ~ 16

Author(s):

Mary Cait McCarthy ◽

Lynne D. Talley ◽

Dean Roemmich

Keyword(s):

Interannual Variability ◽

South Pacific ◽

Subtropical Gyre ◽

Altimeter Data ◽

The South ◽

Expendable Bathythermograph

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Travelling light: Fouling biota on macroplastics arriving on beaches of remote Rapa Nui (Easter Island) in the South Pacific Subtropical Gyre

Marine Pollution Bulletin ◽

10.1016/j.marpolbul.2018.10.015 ◽

2018 ◽

Vol 137 ◽

pp. 119-128 ◽

Cited By ~ 11

Author(s):

Sabine Rech ◽

Martin Thiel ◽

Yaisel J. Borrell Pichs ◽

Eva García-Vazquez

Keyword(s):

South Pacific ◽

Easter Island ◽

Subtropical Gyre ◽

The South ◽

Rapa Nui

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Plastic Pollution in the South Pacific Subtropical Gyre

Plastics Engineering ◽

10.1002/j.1941-9635.2013.tb01006.x ◽

2013 ◽

Vol 69 (5) ◽

pp. 38-44 ◽

Cited By ~ 2

Author(s):

Marcus Eriksen ◽

Anna Cummins ◽

Nikolai Maximenko ◽

Martin Thiel ◽

Gwen Lattin ◽

...

Keyword(s):

South Pacific ◽

Subtropical Gyre ◽

The South ◽

Plastic Pollution

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South Pacific Ocean Dipole: A Predictable Mode on Multiseasonal Time Scales

Journal of Climate ◽

10.1175/jcli-d-13-00293.1 ◽

2014 ◽

Vol 27 (4) ◽

pp. 1648-1658 ◽

Cited By ~ 16

Author(s):

Yuanhong Guan ◽

Jieshun Zhu ◽

Bohua Huang ◽

Zeng-Zhen Hu ◽

James L. Kinter III

Keyword(s):

Pacific Ocean ◽

Time Scales ◽

Southern Oscillation ◽

Austral Summer ◽

South Pacific ◽

The South ◽

Active Centers ◽

Austral Spring ◽

South Pacific Ocean ◽

South Indian

Abstract Evaluating the climate hindcasts for 1982–2009 from the NCEP CFS Reanalysis and Reforecast (CFSRR) project using the Climate Forecast System, version 2 (CFSv2), this study identifies substantial areas of high prediction skill of the sea surface temperature (SST) in the South Pacific. The skill is the highest in the extratropical oceans on seasonal-to-interannual time scales, and it is only slightly lower than that for the El Niño–Southern Oscillation (ENSO). Two regions with the highest prediction skills in the South Pacific in both the CFSv2 and persistence hindcasts coincide with the active centers of opposite signs in the South Pacific Ocean dipole (SPOD) mode, a seesaw between the subtropical and extratropical SST in the South Pacific with a strong phase locking to austral summer. Interestingly, the CFSv2 prediction exhibits skillful predictions made three seasons ahead, more superior to the persistence forecast, suggesting significant dynamical predictability of the SPOD. An austral “spring predictability barrier” is noted in both the dynamical and persistence hindcasts. An analysis of the observational and model data suggests that the SPOD mode is significantly associated with ENSO, as an oceanic response to the atmospheric planetary wave trains forced by the anomalous atmospheric heating in the western Pacific. Although previous studies have demonstrated that the pattern of subtropical SST dipole is ubiquitous in the Southern Ocean, the SPOD has been least known and studied, compared with its counterparts in the south Indian and Atlantic Oceans. Since the SPOD is the most predictable oceanic mode in the whole Southern Hemisphere, its climate effects for local and remote regions should be further studied.

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Influence of mesoscale eddies on the distribution of nitrous oxide in the eastern tropical South Pacific

Biogeosciences ◽

10.5194/bg-13-1105-2016 ◽

2016 ◽

Vol 13 (4) ◽

pp. 1105-1118 ◽

Cited By ~ 9

Author(s):

Damian L. Arévalo-Martínez ◽

Annette Kock ◽

Carolin R. Löscher ◽

Ruth A. Schmitz ◽

Lothar Stramma ◽

...

Keyword(s):

Nitrous Oxide ◽

Water Column ◽

Coastal Upwelling ◽

Mesoscale Eddies ◽

South Pacific ◽

N Cycling ◽

Gene Marker ◽

N Loss ◽

Mode Water ◽

N2o Production

Abstract. Recent observations in the eastern tropical South Pacific (ETSP) have shown the key role of meso- and submesoscale processes (e.g. eddies) in shaping its hydrographic and biogeochemical properties. Off Peru, elevated primary production from coastal upwelling in combination with sluggish ventilation of subsurface waters fuels a prominent oxygen minimum zone (OMZ). Given that nitrous oxide (N2O) production–consumption processes in the water column are sensitive to oxygen (O2) concentrations, the ETSP is a region of particular interest to investigate its source–sink dynamics. To date, no detailed surveys linking mesoscale processes and N2O distributions as well as their relevance to nitrogen (N) cycling are available. In this study, we present the first measurements of N2O across three mesoscale eddies (two mode water or anticyclonic and one cyclonic) which were identified, tracked, and sampled during two surveys carried out in the ETSP in November–December 2012. A two-peak structure was observed for N2O, wherein the two maxima coincide with the upper and lower boundaries of the OMZ, indicating active nitrification and partial denitrification. This was further supported by the abundances of the key gene for nitrification, ammonium monooxygenase (amoA), and the gene marker for N2O production during denitrification, nitrite reductase (nirS). Conversely, we found strong N2O depletion in the core of the OMZ (O2 < 5 µmol L−1) to be consistent with nitrite (NO2−) accumulation and low levels of nitrate (NO3−), thus suggesting active denitrification. N2O depletion within the OMZ's core was substantially higher in the centre of mode water eddies, supporting the view that eddy activity enhances N-loss processes off Peru, in particular near the shelf break where nutrient-rich, productive waters from upwelling are trapped before being transported offshore. Analysis of eddies during their propagation towards the open ocean showed that, in general, “ageing” of mesoscale eddies tends to decrease N2O concentrations through the water column in response to the reduced supply of material to fuel N loss, although hydrographic variability might also significantly impact the pace of the production–consumption pathways for N2O. Our results evidence the relevance of mode water eddies for N2O distribution, thereby improving our understanding of the N-cycling processes, which are of crucial importance in times of climate change and ocean deoxygenation.

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