scholarly journals Formation Mechanism of Barrier Layer in the Subtropical Pacific

2015 ◽  
Vol 45 (11) ◽  
pp. 2790-2805 ◽  
Author(s):  
Shota Katsura ◽  
Eitarou Oka ◽  
Kanako Sato
Keyword(s):  
Formation Mechanism ◽  
Barrier Layer ◽  
Seasonal Variations ◽  
Southern Oscillation ◽  
World Ocean ◽  
South Pacific ◽  
Sea Surface ◽  
Layer Depth ◽  
Isothermal Layer ◽  
North And South

AbstractSeasonal and interannual variations of the barrier layer (BL) and its formation mechanism in the subtropical North and South Pacific were investigated by using raw and gridded Argo profiling float data and various surface flux data in 2003–12 and hydrographic section data from the World Ocean Circulation Experiment Hydrographic Programme. BLs detected by raw Argo profiles, which existed within the sea surface salinity (SSS) front located on the equator side of SSS maxima, were thickest and most frequent in winter and had a temporal scale shorter than 10 days, indicating their transient nature. Surface and subsurface processes for the BL formation suggested by previous studies were evaluated. Poleward Ekman advection of fresher water was dominant as the surface freshening process but cannot explain the observed seasonal variations of the BL. Subsurface equatorward intrusion of high-salinity tropical water was too deep to produce salinity stratification within isothermal layers. These results strongly suggest that BLs in the subtropical Pacific are formed mainly through tilting of the SSS front due to the poleward Ekman flow near the sea surface and the equatorward geostrophic flow in the subsurface. This idea is supported by the dominant contribution of the meridional SSS gradient to the meridional sea surface density gradient within the SSS front and the correspondence between the seasonal variations of the BL and isothermal layer depth. On an interannual time scale, the winter BL thickness in the North and South Pacific was related to the Pacific decadal oscillation and the El Niño–Southern Oscillation, respectively, through the intensity of trade winds controlling isothermal layer depth.

Relative Contributions of North and South Pacific Sea Surface Temperature Anomalies to ENSO

2019 ◽  
Vol 124 (12) ◽  
pp. 6222-6237 ◽  
Author(s):  
Ruiqiang Ding ◽  
Yu‐heng Tseng ◽  
Jianping Li ◽  
Cheng Sun ◽  
Fei Xie ◽  
...  
Keyword(s):  
Surface Temperature ◽  
Sea Surface Temperature ◽  
South Pacific ◽  
Sea Surface ◽  
Temperature Anomalies ◽  
Sea Surface Temperature Anomalies ◽  
North And South

scholarly journals Formation Mechanism for Isopycnal Temperature–Salinity Anomalies Propagating from the Eastern South Pacific to the Equatorial Region

2007 ◽  
Vol 20 (7) ◽  
pp. 1305-1315 ◽  
Author(s):  
Masami Nonaka ◽  
Hideharu Sasaki
Keyword(s):  
Formation Mechanism ◽  
General Circulation ◽  
Circulation Model ◽  
South Pacific ◽  
Ocean General Circulation Model ◽  
Equatorial Region ◽  
Sea Surface ◽  
Global Ocean ◽  
Decadal Time Scale ◽  
Isopycnal Surface

Abstract Equatorward propagation of temperature–salinity (or spiciness) anomalies on an isopycnal surface emanating from the eastern subtropical South Pacific and their formation mechanism are investigated based on a hindcast simulation with an eddy-resolving quasi-global ocean general circulation model. Because of density-compensating meridional distributions of temperature and salinity, the meridional density gradient is weak at the sea surface in the eastern subtropical South Pacific. With these mean fields, cool sea surface temperature anomalies (SSTAs) can make the outcrop line of an isopycnal surface migrate equatorward more than 5° and induce warm and salty anomalies on the isopycnal surface. Subducted warm, salty anomalies propagate to the equatorial region over approximately 5 yr and may influence equatorial isopycnal temperature–salinity anomalies. Although the associated effects are unclear, if these anomalies could further induce warm eastern equatorial SSTAs that are positively correlated with eastern South Pacific SSTAs, opposite sign temperature–salinity anomalies would be formed in the subtropical South Pacific, and a closed cycle having a decadal time scale might be induced.

scholarly journals Investigating the effect of El Niño on nitrous oxide distribution in the Eastern Tropical South Pacific

2018 ◽  
Author(s):  
Qixing Ji ◽  
Mark A. Altabet ◽  
Hermann W. Bange ◽  
Michelle I. Graco ◽  
Xiao Ma ◽  
...  
Keyword(s):  
Nitrous Oxide ◽  
El Niño ◽  
El Nino ◽  
Southern Oscillation ◽  
South Pacific ◽  
Biological Properties ◽  
Nitrite Reduction ◽  
Sea Surface ◽  
N2o Production ◽  
Annual Variations

Abstract. The open ocean is a major source of atmospheric warming and ozone depleting gas nitrous oxide (N2O). Intense sea-to-air fluxes of N2O occur in major oceanic upwelling regions such as the Eastern Tropical South Pacific Ocean (ETSP). The ETSP is influenced by the El Niño-Southern Oscillation that leads to inter-annual variations of physical, chemical and biological properties. A strong El Niño was developing in this region in October 2015, during which we investigated the N2O production pathways and, by comparing to previous non-El Niño years, the effects of El Niño on water column N2O distributions and fluxes. Analysis of N2O natural abundance isotopomers suggested that both nitrification and partial denitrification (nitrate and nitrite reduction to N2O) were important N2O production pathways. Higher than normal sea-surface temperatures were associated with a deepening of the oxycline, while the level of sea surface N2O supersaturation on the continental shelf was nearly an order of magnitude lower than those of non-El Niño years. Therefore, a significant reduction of N2O efflux in the ETSP occurred during the 2015 El Niño event. At both offshore and coastal stations, the N2O concentration profiles during El Niño showed moderate N2O concentration gradients, and peak N2O concentrations were deeper than during non-El Niño years; this was likely the result of suppressed upwelling retaining N2O in subsurface waters. The depth-integrated N2O concentrations during El Niño were nearly twice as high as those measured in non-El Niño years, indicating subsurface N2O during El Niño could be a reservoir for intense N2O effluxes when normal upwelling is resumed after El Niño.

Three Types of South Pacific Subtropical Mode Waters: Their Relation to the Large-Scale Circulation of the South Pacific Subtropical Gyre and Their Temporal Variability

2007 ◽  
Vol 37 (10) ◽  
pp. 2478-2490 ◽  
Author(s):  
Takamasa Tsubouchi ◽  
Toshio Suga ◽  
Kimio Hanawa
Keyword(s):  
World Ocean ◽  
South Pacific ◽  
Recirculation Region ◽  
The South ◽  
Short Term ◽  
The West ◽  
The North ◽  
Term Variation ◽  
North And South

Abstract A detailed spatial distribution of South Pacific Subtropical Mode Water (SPSTMW) and its temporal variation were investigated using the World Ocean Atlas (WOA) 2001 climatology and high-resolution expendable bathythermograph (HRX) line data. In the WOA 2001 climatology, SPSTMW can be classified into western and eastern parts. A detailed examination of spatial distributions using HRX-PX06 line data revealed that the eastern part can be further divided into two types by the Tasman Front (TF) extension. Consequently, SPSTMW can be classified into three types, referred to in the present study as the West, North, and South types. The West type, situated in the recirculation region of the East Australia Current (EAC), has a core layer temperature (CLT) of about 19.1°C; the North type, in the region north of the TF extension, has a CLT of about 17.6°C; and the South type, in the region south of the TF extension, has a CLT of about 16.0°C. The long-term (>6 yr) variations in the inventories of the three types were dissimilar to each other. The short-term (<6 yr) and long-term variations in the mean CLT of the North and South types were greater than that of the West type. Winter cooling in the previous year may have influenced the short-term variation in the South-type CLT. Moreover, the strength of the EAC may have influenced long-term variation in the West-type inventory and thickness and in the North-type thickness and CLT.

Decadal Spinup of the South Pacific Subtropical Gyre

2007 ◽  
Vol 37 (2) ◽  
pp. 162-173 ◽  
Author(s):  
D. Roemmich ◽  
J. Gilson ◽  
R. Davis ◽  
P. Sutton ◽  
S. Wijffels ◽  
...  
Keyword(s):  
Ocean Circulation ◽  
World Ocean ◽  
South Pacific ◽  
Sea Surface Height ◽  
Subtropical Gyre ◽  
Sea Surface ◽  
The South ◽  
Maximum Increase ◽  
Large Spatial Scale ◽  
Dynamic Height

Abstract An increase in the circulation of the South Pacific Ocean subtropical gyre, extending from the sea surface to middepth, is observed over 12 years. Datasets used to quantify the decadal gyre spinup include satellite altimetric height, the World Ocean Circulation Experiment (WOCE) hydrographic and float survey of the South Pacific, a repeated hydrographic transect along 170°W, and profiling float data from the global Argo array. The signal in sea surface height is a 12-cm increase between 1993 and 2004, on large spatial scale centered at about 40°S, 170°W. The subsurface datasets show that this signal is predominantly due to density variations in the water column, that is, to deepening of isopycnal surfaces, extending to depths of at least 1800 m. The maximum increase in dynamic height is collocated with the deep center of the subtropical gyre, and the signal represents an increase in the total counterclockwise geostrophic circulation of the gyre, by at least 20% at 1000 m. A comparison of WOCE and Argo float trajectories at 1000 m confirms the gyre spinup during the 1990s. The signals in sea surface height, dynamic height, and velocity all peaked around 2003 and subsequently began to decline. The 1990s increase in wind-driven circulation resulted from decadal intensification of wind stress curl east of New Zealand—variability associated with an increase in the atmosphere’s Southern Hemisphere annular mode. It is suggested (based on altimetric height) that midlatitude gyres in all of the oceans have been affected by variability in the atmospheric annular modes on decadal time scales.

scholarly journals Resurfacing of South Pacific Tropical Water in the Equatorial Pacific and Its Variability Associated with ENSO

2017 ◽  
Vol 47 (5) ◽  
pp. 1095-1106 ◽  
Author(s):  
Tangdong Qu ◽  
Shan Gao
Keyword(s):  
Southern Oscillation ◽  
South Pacific ◽  
Equatorial Pacific ◽  
Sea Surface ◽  
Sea Surface Salinity ◽  
Freshwater Flux ◽  
Surface Salinity ◽  
Tropical Water ◽  
Analysis Of Results ◽  
South Pacific Tropical Water

AbstractAnalysis of results from a simulated passive tracer confirms the resurfacing of South Pacific Tropical Water in the equatorial Pacific. Over the period of integration (1993–2011), both the volume and barycenter of the South Pacific Tropical Water that resurfaces in the equatorial Pacific are tightly linked to El Niño–Southern Oscillation (ENSO), with their correlation with the Niño-3.4 index reaching −0.79 and 0.84, respectively. Their correlation (−0.75 and 0.85) with the sea surface salinity index, Niño-S34.8, is also high. Of particular interest is that both the volume and barycenter of the resurfacing South Pacific Tropical Water peak earlier than the ENSO indices by about 3 months. On the interannual time scale, the resurfacing of South Pacific Tropical Water may modulate the sea surface salinity in the equatorial Pacific at a rate equivalent to as much as 25% of the surface freshwater flux. The results suggest that the resurfacing of South Pacific Tropical Water directly contributes to the sea surface salinity variability in the equatorial Pacific and potentially plays a role in ENSO evolution.

scholarly journals Observations of Interannual Equatorial Freshwater Jets in the Western Pacific

2015 ◽  
Vol 45 (11) ◽  
pp. 2848-2865 ◽  
Author(s):  
Xiaolin Zhang ◽  
Allan J. Clarke
Keyword(s):  
Sea Level ◽  
El Niño ◽  
El Nino ◽  
Southern Oscillation ◽  
Sea Surface ◽  
Altimeter Data ◽  
Surface Salinity ◽  
Near Surface ◽  
Meridional Gradient ◽  
Isothermal Layer

AbstractObservations of TRITON moored array salinity and temperature in the very wet western equatorial Pacific at 137°E, 147°E, and 156°E since the late 1990s reveal the importance of rainfall to the interannual flow and El Niño–Southern Oscillation (ENSO) dynamics. Past work has shown that in this region a fresher surface isohaline layer is embedded in a thicker isothermal layer. Array estimates of dynamic height relative to the 50–70-m isothermal layer depth (ILD) indicate a near-surface salinity-driven contribution to the monthly sea level anomaly that is uncorrelated with, and smaller than, monthly anomalous sea surface height (SSH) estimated from altimeter data. Despite the smaller size of , its meridional gradient dominates the total sea level meridional gradient. Thus, the corresponding shallow equatorially trapped interannual freshwater jet dominates the near-surface zonal interannual flow. This jetlike flow has a meridional scale of only about 2°–3° of latitude, an amplitude of 23 cm s−1, and is associated with the zonal back and forth displacement of the western equatorial warm/fresh pool that is fundamental to El Niño. The jet is not directly forced by the interannual freshwater surface flux but rather by wind stress anomalies that are mostly east of the warm/fresh pool edge during La Niña and mostly west of it during El Niño. A conceptual coupled ocean–atmosphere instability model is proposed to understand these observations. Calculations show that Aquarius satellite sea surface salinity (SSS) data match the TRITON in situ data well and that the satellite SSS can be used to estimate , and hence , geostrophically.

Relative contributions of North and South Pacific sea surface temperature anomalies to ENSO

2020 ◽  
Author(s):  
Ruiqiang Ding ◽  
Yu-heng Tseng ◽  
Jianping Li
Keyword(s):  
Surface Temperature ◽  
Sea Surface Temperature ◽  
Southern Oscillation ◽  
South Pacific ◽  
Sea Surface ◽  
Coupling Mechanism ◽  
The South ◽  
Enso Events ◽  
The North ◽  
Sst Forcing

<p>Variations in the sea surface temperature (SST) field in both the North Pacific [represented by the Victoria mode (VM)] and the South Pacific [represented by the South Pacific Quadrapole (SPQ) mode] are related to the state of the El Niño-Southern Oscillation (ENSO) three seasons later. Here, with the aid of observational data and numerical experiments, we demonstrate that both VM and SPQ SST forcing can influence the development of ENSO events through a similar air–sea coupling mechanism. By comparing ENSO amplitudes induced by the VM and SPQ, as well as the percentages of strong ENSO events followed by the VM and SPQ events, we find that the VM and SPQ make comparable contributions and therefore have similar levels of importance to ENSO. Additional analysis indicates that although VM or SPQ SST forcing alone may serve as a good predictor for ENSO events, it is more effective to consider their combined influence. A prediction model based on both VM and SPQ indices is developed, which is capable of yielding skillful forecasts for ENSO at lead times of three seasons.</p>

scholarly journals Interannual Variability and Trends in Sea Surface Temperature, Lower and Middle Atmosphere Temperature at Different Latitudes for 1980–2019

Atmosphere ◽  
2021 ◽  
Vol 12 (4) ◽  
pp. 454
Author(s):  
Andrew R. Jakovlev ◽  
Sergei P. Smyshlyaev ◽  
Vener Y. Galin
Keyword(s):  
Surface Temperature ◽  
Sea Surface Temperature ◽  
Lower Stratosphere ◽  
Middle Atmosphere ◽  
Southern Oscillation ◽  
Lower Troposphere ◽  
Reanalysis Data ◽  
Sea Surface ◽  
The Arctic ◽  
The Impact

The influence of sea-surface temperature (SST) on the lower troposphere and lower stratosphere temperature in the tropical, middle, and polar latitudes is studied for 1980–2019 based on the MERRA2, ERA5, and Met Office reanalysis data, and numerical modeling with a chemistry-climate model (CCM) of the lower and middle atmosphere. The variability of SST is analyzed according to Met Office and ERA5 data, while the variability of atmospheric temperature is investigated according to MERRA2 and ERA5 data. Analysis of sea surface temperature trends based on reanalysis data revealed that a significant positive SST trend of about 0.1 degrees per decade is observed over the globe. In the middle latitudes of the Northern Hemisphere, the trend (about 0.2 degrees per decade) is 2 times higher than the global average, and 5 times higher than in the Southern Hemisphere (about 0.04 degrees per decade). At polar latitudes, opposite SST trends are observed in the Arctic (positive) and Antarctic (negative). The impact of the El Niño Southern Oscillation phenomenon on the temperature of the lower and middle atmosphere in the middle and polar latitudes of the Northern and Southern Hemispheres is discussed. To assess the relative influence of SST, CO2, and other greenhouse gases’ variability on the temperature of the lower troposphere and lower stratosphere, numerical calculations with a CCM were performed for several scenarios of accounting for the SST and carbon dioxide variability. The results of numerical experiments with a CCM demonstrated that the influence of SST prevails in the troposphere, while for the stratosphere, an increase in the CO2 content plays the most important role.

scholarly journals On the robustness of an eastern boundary upwelling ecosystem exposed to multiple stressors

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Ndague Diogoul ◽  
Patrice Brehmer ◽  
Hervé Demarcq ◽  
Salaheddine El Ayoubi ◽  
Abou Thiam ◽  
...  
Keyword(s):  
Multiple Stressors ◽  
Marine Ecosystem ◽  
Trophic Levels ◽  
Sea Surface ◽  
Relative Index ◽  
Upwelling System ◽  
The North ◽  
Latitudinal Shift ◽  
Large Marine Ecosystem ◽  
North And South

AbstractThe resistance of an east border upwelling system was investigated using relative index of marine pelagic biomass estimates under a changing environment spanning 20-years in the strongly exploited southern Canary Current Large marine Ecosystem (sCCLME). We divided the sCCLME in two parts (north and south of Cap Blanc), based on oceanographic regimes. We delineated two size-based groups (“plankton” and “pelagic fish”) corresponding to lower and higher trophic levels, respectively. Over the 20-year period, all spatial remote sensing environmental variables increased significantly, except in the area south of Cap Blanc where sea surface Chlorophyll-a concentrations declined and the upwelling favorable wind was stable. Relative index of marine pelagic abundance was higher in the south area compared to the north area of Cap Blanc. No significant latitudinal shift to the mass center was detected, regardless of trophic level. Relative pelagic abundance did not change, suggesting sCCLME pelagic organisms were able to adapt to changing environmental conditions. Despite strong annual variability and the presence of major stressors (overfishing, climate change), the marine pelagic ressources, mainly fish and plankton remained relatively stable over the two decades, advancing our understanding on the resistance of this east border upwelling system.

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