Benthic community-water column coupling during the 1982-1983 El Niño. Are community changes at high latitudes attributable to cause or coincidence?1

Abundance and production of the pelagic heterotrophic bacteria community were studied at northern Chile during winter and summer periods of 2006–2007 in relation to seasonal changes in physical and chemical variables, including the influence of a weak El Niño event. Bacterial abundance was estimated by flow cytometry and secondary bacterial production by protein synthesis after bacterial uptake of14C-isoleucine. Bacterial biomass showed high values in the range of 2.84 at 96.6 µ g C l−1d−1with a bacterial growth efficiency (BGE) of 37.4% in the summer of 2007, and 2.7% in the winter of 2006. High amounts of C (~1.2 to 1.8 g C m−2d−1) were used for bacterial respiration in the upper 20 m. Environmental impact on bacterial abundance and BGE was reflected in a positive correlation with phytoplankton biomass (r2 > 0.40P < 0.05), and a lack of correlation with temperature (P > 0.05). Seasonal differences in abundance and BGE were mainly attributed to an ‘abnormally’ warm winter of 2006, which caused a greater stratification of the water column—a weaker and much deeper oxycline. The oxycline is normally shallower (<20 m) in the zone because of the ascent of the oxygen minimum zone (OMZ) upon upwelling. Winter 2006 conditions indicated presence of a weak El Niño event. Bacteria abundance increased during this warming event, but their metabolic activity was drastically reduced, resulting in a very low BGE. Our study suggests that changes from a prevailing sub-oxic to a highly oxygenated water column could have impacted the bacterial community, thus reducing its productive capacity. Therefore, variation in vertical distribution of the OMZ forced by upwelling variability and the El Niño impact might play an important role in the dynamics of the microbial component in this highly productive upwelling system.

Download Full-text

Signals of El Niño Modoki in the tropical tropopause layer and stratosphere

Atmospheric Chemistry and Physics ◽

10.5194/acp-12-5259-2012 ◽

2012 ◽

Vol 12 (11) ◽

pp. 5259-5273 ◽

Cited By ~ 85

Author(s):

F. Xie ◽

J. Li ◽

W. Tian ◽

J. Feng ◽

Y. Huo

Keyword(s):

Water Vapor ◽

El Niño ◽

El Nino ◽

Polar Vortex ◽

High Latitudes ◽

Tropical Tropopause Layer ◽

El Niño Modoki ◽

Tropical Tropopause ◽

El Niño Events ◽

El Nino Events

Abstract. The effects of El Niño Modoki events on the tropical tropopause layer (TTL) and on the stratosphere were investigated using European Center for Medium Range Weather Forecasting (ECMWF) reanalysis data, oceanic El Niño indices, and general climate model outputs. El Niño Modoki events tend to depress convective activities in the western and eastern Pacific but enhance convective activities in the central and northern Pacific. Consequently, during El Niño Modoki events, negative water vapor anomalies occur in the western and eastern Pacific upper troposphere, whereas there are positive anomalies in the central and northern Pacific upper troposphere. The spatial patterns of the outgoing longwave radiation (OLR) and upper tropospheric water vapor anomalies exhibit a tripolar form. The empirical orthogonal function (EOF) analysis of the OLR and upper tropospheric water vapor anomalies reveals that canonical El Niño events are associated with the leading mode of the EOF, while El Niño Modoki events correspond to the second mode. The composite analysis based on ERA-interim data indicate that El Niño Modoki events have a reverse effect on middle-high latitudes stratosphere, as compared with the effect of typical El Niño events, i.e., the northern polar vortex is stronger and colder but the southern polar vortex is weaker and warmer during El Niño Modoki events. According to the simulation' results, we found that the reverse effect on the middle-high latitudes stratosphere is resulted from a complicated interaction between quasi-biennial oscillation (QBO) signal of east phase and El Niño Modoki signal. This interaction is not a simply linear overlay of QBO signal and El Niño Modoki signal in the stratosphere, it is El Niño Modoki that leads to different tropospheric zonal wind anomalies with QBO forcing from that caused by typical El Niño, thus, the planetary wave propagation from troposphere to the stratosphere during El Niño Modoki events is different from that during canonical El Niño events. However, when QBO is in its west phase, El Niño Modoki events have the same effect on middle-high latitudes stratosphere as the typical El Niño events. Our simulations also suggest that canonical El Niño and El Niño Modoki activities actually have the same influence on the middle-high latitudes stratosphere when in the absence of QBO forcing.

Download Full-text

Seasonal and interannual variability of water column properties along the Rottnest continental shelf, south-west Australia

10.5194/os-2018-115 ◽

2018 ◽

Author(s):

Miaoju Chen ◽

Charitha B. Pattiaratchi ◽

Anas Ghadouani ◽

Christine Hanson

Keyword(s):

Chlorophyll Fluorescence ◽

Continental Shelf ◽

Water Column ◽

El Niño ◽

El Nino ◽

Strong Wind ◽

South West ◽

Sea Bed ◽

Basin Scale ◽

Autumn And Winter

Abstract. A multiyear, ocean glider dataset, obtained along a representative cross-shelf transect along the Rottnest continental shelf, south-west Australia, was used to characterise the seasonal and inter-annual variability of water column properties (temperature, salinity, and chlorophyll fluorescence distribution). All three variables showed distinct seasonal and inter-annual variations. Local and basin-scale ocean–atmosphere processes also affected the spatial distributions of the water column properties. The controlling influences for the variability were derived from (a) at the local scale, the Leeuwin Current and dense shelf water cascades (DSWC); and, (2) at the basin scale, the El Niño Southern Oscillation (ENSO). In spring and summer, shallow waters were well mixed due to strong wind mixing and the deeper waters (> 50 m) were vertically stratified in temperature that contributed to the formation of a subsurface chlorophyll maximum (SCM). With the onset of storms in late autumn, the water column was well mixed with the SCM absent. On the inner shelf, chlorophyll fluorescence concentrations were highest in autumn and winter; DSWCs were also the main physical feature during autumn and winter. Chlorophyll fluorescence concentration was higher closer to the sea bed than at the surface in spring, summer, and autumn. The seasonal patterns coincided with changes in the wind field (weaker winds in autumn) and air–sea fluxes (winter cooling and summer evaporation). Inter-annual variation was associated with ENSO events. Lower temperatures, higher salinity, and higher chlorophyll fluorescence (> 1 mg m−3) were associated with the El Niño event in 2010. During the strong La Niña event in 2011, temperatures increased (a marine heat wave), and salinity and chlorophyll fluorescence decreased (

Download Full-text

Reef Community Changes Associated with the 2009–2010 El Niño in the Southern Mexican Pacific

Pacific Science ◽

10.2984/70.2.4 ◽

2016 ◽

Vol 70 (2) ◽

pp. 175-190 ◽

Cited By ~ 13

Author(s):

Andrés López-Pérez ◽

Sergio Guendulain-García ◽

Rebeca Granja-Fernández ◽

Valeria Hernández-Urraca ◽

Laura Galván-Rowland ◽

...

Keyword(s):

El Niño ◽

El Nino ◽

Mexican Pacific ◽

Reef Community ◽

Community Changes

Download Full-text

The response of sound scatterers to El Niño- and La Niña-like oceanographic regimes in the southeastern Atlantic

ICES Journal of Marine Science ◽

10.1093/icesjms/fsp102 ◽

2009 ◽

Vol 66 (6) ◽

pp. 1063-1072 ◽

Cited By ~ 19

Author(s):

Marek Ostrowski ◽

José C. B. da Silva ◽

Bomba Bazik-Sangolay

Keyword(s):

Water Column ◽

Internal Waves ◽

El Niño ◽

El Nino ◽

Thin Layers ◽

La Niña ◽

Tropical Water ◽

La Nina ◽

Radar Imagery ◽

Southeastern Atlantic

Abstract Ostrowski, M., da Silva, J. C. B., and Bazik-Sangolay, B. 2009. The response of sound scatterers to El Niño- and La Niña-like oceanographic regimes in the southeastern Atlantic. – ICES Journal of Marine Science, 66: 1063–1072. Oceanographic conditions off Angola alternate seasonally between upwelling in the austral winter and El Niño-like intrusions and downwelling in summer. During winter in regions deeper than 30 m, the water column consists of a top layer of warm, tropical water overlying cold, nutrient-rich, and hypoxic South Atlantic Central Water (SACW). Closer inshore the water becomes well mixed. In the stratified region, acoustic backscatter at 38 kHz matches the oceanographic structure. It is strong in the top layer, but declines sharply in the SACW. During summer, the water column is continuously stratified, and the SACW is absent from the shelf. The backscatter reveals multiple thin layers extending across much of the shelf. The scattering layers are often perturbed by internal waves. The combined evidence from multiple acoustic surveys and the existing synthetic-aperture radar imagery suggests that tidal internal waves are a pervasive phenomenon in Angolan waters.

Download Full-text

Investigating the effect of El Niño on nitrous oxide distribution in the eastern tropical South Pacific

Biogeosciences ◽

10.5194/bg-16-2079-2019 ◽

2019 ◽

Vol 16 (9) ◽

pp. 2079-2093 ◽

Cited By ~ 2

Author(s):

Qixing Ji ◽

Mark A. Altabet ◽

Hermann W. Bange ◽

Michelle I. Graco ◽

Xiao Ma ◽

...

Keyword(s):

Nitrous Oxide ◽

Water Column ◽

El Niño ◽

El Nino ◽

Southern Oscillation ◽

South Pacific ◽

Biological Properties ◽

Nitrite Reduction ◽

N2o Production ◽

Near Surface

Abstract. The open ocean is a major source of nitrous oxide (N2O), an atmospheric trace gas attributable to global warming and ozone depletion. Intense sea-to-air N2O fluxes occur in major oceanic upwelling regions such as the eastern tropical South Pacific (ETSP). The ETSP is influenced by the El Niño–Southern Oscillation that leads to inter-annual variations in physical, chemical, and biological properties in the water column. In October 2015, a strong El Niño event was developing in the ETSP; we conduct field observations to investigate (1) the N2O production pathways and associated biogeochemical properties and (2) the effects of El Niño on water column N2O distributions and fluxes using data from previous non-El Niño years. Analysis of N2O natural abundance isotopomers suggested that nitrification and partial denitrification (nitrate and nitrite reduction to N2O) were occurring in the near-surface waters; indicating that both pathways contributed to N2O effluxes. Higher-than-normal sea surface temperatures were associated with a deepening of the oxycline and the oxygen minimum layer. Within the shelf region, surface N2O supersaturation was nearly an order of magnitude lower than that of non-El Niño years. Therefore, a significant reduction of N2O efflux (75 %–95 %) in the ETSP occurred during the 2015 El Niño. At both offshore and coastal stations, the N2O concentration profiles during El Niño showed moderate N2O concentration gradients, and the peak N2O concentrations occurred at deeper depths during El Niño years; this was likely the result of suppressed upwelling retaining N2O in subsurface waters. At multiple stations, water-column inventories of N2O within the top 1000 m were up to 160 % higher than those measured in non-El Niño years, indicating that subsurface N2O during El Niño could be a reservoir for intense N2O effluxes when normal upwelling is resumed after El Niño.

Download Full-text