scholarly journals Tropical deoxygenation sites revisited to investigate oxygen and nutrient trends

Ocean Science ◽  
2021 ◽  
Vol 17 (3) ◽  
pp. 833-847
Author(s):  
Lothar Stramma ◽  
Sunke Schmidtko
Keyword(s):  
Time Series ◽  
Indian Ocean ◽  
Tropical Indian Ocean ◽  
Equatorial Pacific ◽  
Equatorial Pacific Ocean ◽  
Low Oxygen ◽  
Biological Communities ◽  
Pelagic Habitat ◽  
Ocean Layer ◽  
Historic Data

Abstract. An oxygen decrease of the intermediate-depth low-oxygen zones (300 to 700 m) is seen in time series for selected tropical areas for the period 1960 to 2008 in the eastern tropical Atlantic, the equatorial Pacific and the eastern tropical Indian Ocean. These nearly 5-decade time series were extended to 68 years by including rare historic data starting in 1950 and more recent data. For the extended time series between 1950 and 2018, the deoxygenation trend for the layer 300 to 700 m is similar to the deoxygenation trend seen in the shorter time series. Additionally, temperature, salinity, and nutrient time series in the upper-ocean layer (50 to 300 m) of these areas were investigated since this layer provides critical pelagic habitat for biological communities. Due to the low amount of data available, the results are often not statistically significant within the 95 % confidence interval but nevertheless indicate trends worth discussing. Generally, oxygen is decreasing in the 50 to 300 m layer, except for an area in the eastern tropical South Atlantic. Nutrients also showed long-term trends in the 50 to 300 m layer in all ocean basins and indicate overlying variability related to climate modes. Nitrate increased in all areas. Phosphate also increased in the Atlantic Ocean and Indian Ocean areas, while it decreased in the two areas of the equatorial Pacific Ocean. Silicate decreased in the Atlantic and Pacific areas but increased in the eastern Indian Ocean. Hence, oxygen and nutrients show trends in the tropical oceans, though nutrients trends are more variable between ocean areas than the oxygen trends; therefore, we conclude that those trends are more dependent on local drivers in addition to a global trend. Different positive and negative trends in temperature, salinity, oxygen and nutrients indicate that oxygen and nutrient trends cannot be completely explained by local warming.

scholarly journals Oxygen and nutrient trends in the Tropical Oceans

2020 ◽  
Author(s):  
Lothar Stramma ◽  
Sunke Schmidtko
Keyword(s):  
Time Series ◽  
Indian Ocean ◽  
Tropical Indian Ocean ◽  
Equatorial Pacific ◽  
Equatorial Pacific Ocean ◽  
Low Oxygen ◽  
Biological Communities ◽  
Tropical Oceans ◽  
Pelagic Habitat ◽  
Ocean Layer

Abstract. A vertical expansion of the intermediate-depth low-oxygen zones (300 to 700 m) is seen in time series for selected tropical areas for the period 1960 to 2008, in the eastern tropical Atlantic, the equatorial Pacific and the eastern tropical Indian Ocean. These nearly five decade-long time series were extended to 68 years by including rare historic data starting in 1950 and more recent data. For the extended time series between 1950 and 2018 the deoxygenation trend for the layer 300 to 700 m is similar to the deoxygenation trend seen in the shorter time series. Additionally, temperature, salinity and nutrient time series in the upper ocean layer (50 to 300 m) of these areas were investigated since this layer provides critical pelagic habitat for biological communities. Generally, oxygen is decreasing in the 50 to 300 m layer except for an area in the eastern tropical South Atlantic. Nutrients also showed long-term trends in the 50 to 300 m layer in all ocean basins and indicates overlying variability related to climate modes. Nitrate increased in all areas. Phosphate also increased in the Atlantic and Indian Ocean areas, while it decreased in the two areas of the equatorial Pacific Ocean. Silicate decreased in the Atlantic and Pacific areas but increased in the eastern Indian Ocean. Hence oxygen and nutrients show trends in the tropical oceans, though nutrients trends are more variable between ocean areas than the oxygen trends, therefore we conclude that those trends are more dependent on local drivers in addition to a global trend. Different positive and negative trends in temperature, salinity, oxygen and nutrients indicate that oxygen and nutrient trends cannot be completely explained by local warming.

scholarly journals Forcing of the Indian Ocean Dipole on the Interannual Variations of the Tropical Pacific Ocean: Roles of the Indonesian Throughflow

2011 ◽  
Vol 24 (14) ◽  
pp. 3593-3608 ◽  
Author(s):  
Dongliang Yuan ◽  
Jing Wang ◽  
Tengfei Xu ◽  
Peng Xu ◽  
Zhou Hui ◽  
...  
Keyword(s):  
Pacific Ocean ◽  
Indian Ocean ◽  
Indian Ocean Dipole ◽  
Tropical Pacific ◽  
Equatorial Pacific ◽  
Indonesian Throughflow ◽  
Tropical Pacific Ocean ◽  
Equatorial Pacific Ocean ◽  
The Indian Ocean ◽  
The Tropical Pacific

Abstract Controlled numerical experiments using ocean-only and ocean–atmosphere coupled general circulation models show that interannual sea level depression in the eastern Indian Ocean during the Indian Ocean dipole (IOD) events forces enhanced Indonesian Throughflow (ITF) to transport warm water from the upper-equatorial Pacific Ocean to the Indian Ocean. The enhanced transport produces elevation of the thermocline and cold subsurface temperature anomalies in the western equatorial Pacific Ocean, which propagate to the eastern equatorial Pacific to induce significant coupled evolution of the tropical Pacific oceanic and atmospheric circulation. Analyses suggest that the IOD-forced ITF transport anomalies are about the same amplitudes as those induced by the Pacific ENSO. Results of the coupled model experiments suggest that the anomalies induced by the IOD persist in the equatorial Pacific until the year following the IOD event, suggesting the importance of the oceanic channel in modulating the interannual climate variations of the tropical Pacific Ocean at the time lag beyond one year.

scholarly journals Interannual Climate Variability over the Tropical Pacific Ocean Induced by the Indian Ocean Dipole through the Indonesian Throughflow

2013 ◽  
Vol 26 (9) ◽  
pp. 2845-2861 ◽  
Author(s):  
Dongliang Yuan ◽  
Hui Zhou ◽  
Xia Zhao
Keyword(s):  
Pacific Ocean ◽  
Indian Ocean ◽  
Tropical Indian Ocean ◽  
Sea Surface Height ◽  
Equatorial Pacific ◽  
Sea Surface ◽  
Indonesian Throughflow ◽  
Cold Tongue ◽  
The Indian Ocean ◽  
Southeastern Tropical Indian Ocean

Abstract The authors’ previous dynamical study has suggested a link between the Indian and Pacific Ocean interannual climate variations through the transport variations of the Indonesian Throughflow. In this study, the consistency of this oceanic channel link with observations is investigated using correlation analyses of observed ocean temperature, sea surface height, and surface wind data. The analyses show significant lag correlations between the sea surface temperature anomalies (SSTA) in the southeastern tropical Indian Ocean in fall and those in the eastern Pacific cold tongue in the following summer through fall seasons, suggesting potential predictability of ENSO events beyond the period of 1 yr. The dynamics of this teleconnection seem not through the atmospheric bridge, because the wind anomalies in the far western equatorial Pacific in fall have insignificant correlations with the cold tongue anomalies at time lags beyond one season. Correlation analyses between the sea surface height anomalies (SSHA) in the southeastern tropical Indian Ocean and those over the Indo-Pacific basin suggest eastward propagation of the upwelling anomalies from the Indian Ocean into the equatorial Pacific Ocean through the Indonesian Seas. Correlations in the subsurface temperature in the equatorial vertical section of the Pacific Ocean confirm the propagation. In spite of the limitation of the short time series of observations available, the study seems to suggest that the ocean channel connection between the two basins is important for the evolution and predictability of ENSO.

ENSO response to changes in the tropical Indian ocean temperature

2021 ◽  
Author(s):  
Brady Ferster ◽  
Alexey Fedorov ◽  
Juliette Mignot ◽  
Eric Guilyardi
Keyword(s):  
Indian Ocean ◽  
Southern Oscillation ◽  
Coupled Model ◽  
Tropical Indian Ocean ◽  
Equatorial Pacific ◽  
Central Pacific ◽  
Trade Winds ◽  
Enso Variability ◽  
The Mean ◽  
Ensemble Experiments

<p>Since the start of the 21st century, El Niño-Southern Oscillation (ENSO) variability has changed, supporting generally weaker Central Pacific El Niño events. Recent studies suggest that stronger trade winds in the equatorial Pacific could be a key driving force contributing to this shift. One possible mechanism to drive such changes in the mean tropical Pacific climate state is the enhanced warming trends in the tropical Indian Ocean (TIO) relative to the rest of the tropics. TIO warming can affect the Walker circulation in both the Pacific and Atlantic basins by inducing quasi-stationary Kelvin and Rossby wave patterns. Using the latest coupled-model from Insitut Pierre Simon Laplace (IPSL-CM6), ensemble experiments are conducted to investigate the effect of TIO sea surface temperature (SST) on ENSO variability. Applying a weak SST nudging over the TIO region, in four ensemble experiments we change mean Indian ocean SST by -1.4°C, -0.7°C, +0.7°C, and +1.4°C and find that TIO warming changes the magnitude of the mean equatorial Pacific zonal wind stress proportionally to the imposed forcing, with stronger trades winds corresponding to a warmer TIO. Surprisingly, ENSO variability increases in both TIO cooling and warming experiments, relative to the control. While a stronger ENSO for weaker trade winds, associated with TIO cooling, is expected from previous studies, we argue that the ENSO strengthening for stronger trade winds, associated with TIO cooling, is related to the induced changes in ocean stratification. We illustrate this effect by computing different contributions to the Bjerknes stability index. Thus, our results suggest that the tropical Indian ocean temperatures are an important regulator of TIO mean state and ENSO dynamics.</p>

scholarly journals Potential Impact of the Tropical Indian Ocean–Indonesian Seas on El Niño Characteristics*

2010 ◽  
Vol 23 (14) ◽  
pp. 3933-3952 ◽  
Author(s):  
H. Annamalai ◽  
Shinichiro Kida ◽  
Jan Hafner
Keyword(s):  
Indian Ocean ◽  
El Niño ◽  
El Nino ◽  
Tropical Indian Ocean ◽  
Equatorial Pacific ◽  
Western Pacific ◽  
Abrupt Increase ◽  
Indonesian Seas ◽  
Class 1 ◽  
Sst Anomalies

Abstract Diagnostics performed with twentieth-century (1861–2000) ensemble integrations of the Geophysical Fluid Dynamics Laboratory Climate Model, version 2.1 (CM2.1) suggest that, during the developing phase, El Niño events that co-occur with the Indian Ocean Dipole Zonal Mode (IODZM; class 1) are stronger than those without (class 2). Also, during class 1 events coherent sea surface temperature (SST) anomalies develop in the Indonesian seas that closely follow the life cycle of IODZM. This study investigates the effect of these regional SST anomalies (equatorial Indian Ocean and Indonesian seas) on the amplitude of the developing El Niño. An examination of class 1 minus class 2 composites suggests two conditions that could lead to a strong El Niño in class 1 events: (i) during January, ocean–atmosphere conditions internal to the equatorial Pacific are favorable for the development of a stronger El Niño and (ii) during May–June, coinciding with the development of regional SST anomalies, an abrupt increase in westerly wind anomalies is noticeable over the equatorial western Pacific with a subsequent increase in thermocline and SST anomalies over the eastern equatorial Pacific. This paper posits the hypothesis that, under favorable conditions in the equatorial Pacific, regional SST anomalies may enable the development of a stronger El Niño. Owing to a wealth of feedbacks in CM2.1, solutions from a linear atmosphere model forced with May–June anomalous precipitation and anomalous SST from selected areas over the equatorial Indo-Pacific are examined. Consistent with our earlier study, the net Kelvin wave response to contrasting tropical Indian Ocean heating anomalies cancels over the equatorial western Pacific. In contrast, Indonesian seas SST anomalies account for about 60%–80% of the westerly wind anomalies over the equatorial western Pacific and also induce anomalous precipitation over the equatorial central Pacific. It is argued that the feedback between the precipitation and circulation anomalies results in an abrupt increase in zonal wind anomalies over the equatorial western Pacific. Encouraged by these results, the authors further examined the processes that cause cold SST anomalies over the Indonesian seas using an ocean model. Sensitivity experiments suggest that local wind anomalies, through stronger surface heat loss and evaporation, and subsurface upwelling are the primary causes. The present results imply that in coupled models, a proper representation of regional air–sea interactions over the equatorial Indo-Pacific warm pool may be important to understand and predict the amplitude of El Niño.

scholarly journals The distribution and variability of chlorophyll-a bloom in the southeastern tropical Indian Ocean using Empirical Orthogonal Function analysis

2017 ◽  
Vol 18 (4) ◽  
pp. 1546-1555
Author(s):  
ISKHAQ ISKANDAR ◽  
QURNIA WULAN SARI ◽  
DEDI SETIABUDIDAYA ◽  
INDRA YUSTIAN ◽  
BRUCE MONGER
Keyword(s):  
Time Series ◽  
Indian Ocean ◽  
Chlorophyll A ◽  
Empirical Orthogonal Function ◽  
Function Analysis ◽  
Principal Component ◽  
Tropical Indian Ocean ◽  
Ekman Pumping ◽  
Orthogonal Function ◽  
Southeastern Tropical Indian Ocean

Iskandar I, Sari QW, Setiabudidaya D, Yustian I, Monger B. 2017. The distribution and variability of chlorophyll-a bloom in the southeastern tropical Indian Ocean using Empirical Orthogonal Function analysis. Biodiversitas 18: 1546-1555. The Indian Ocean Dipole (IOD) events cause anomalously strong upwelling along the sourthen coast of Sumatra-Java leading to the bloom of chlorophylla. An empirical orthogonal function (EOF) analysis was applied to the time series of the satellite-observed chlorophyll-a, sea surface temperature (SST) and surface winds. Spatial eigen functions of the first EOF mode revealed the broad areas of coherent temporal variation in chlorophyll-a, SST and Ekman pumping, which was observed in the southeastern tropical Indian Ocean (SETIO) region. The corresponding time series of principal component of the first EOF mode revealed a robust seasonal variation and relativley weak inter-annual variation. The second EOF mode exhibited a distinct inter-annual variation with the high surface chlorophyll-a concentration was observed along the southern coast of Sumatra-Java. This high chlorophyll-a concentration is co-located with the low SST, the positive Ekman pumping, and the positive wind-induced mixing. An EOF analysis applied on the seasonal time series showed interesting patterns. The leading EOF mode during the peak IOD season from September to November (SON) showed the high concentration of chlorophyll-a was restricted to the southern coast of Java and was co-located with low SST region. The corresponding time series of principal component of the leading EOF mode showed a significant correlation with the Dipole Mode Index (DMI), however it had no correlation with the Ekman pumping. It could be concluded that the chlorophyll-a bloom during the peak phase of the IOD event was generated by the alongshore upwelling-favorable winds in the preceding season.

Interdecadal Changes of 30-Yr SST Normals during 1871–2000

2003 ◽  
Vol 16 (10) ◽  
pp. 1601-1612 ◽  
Author(s):  
Yan Xue ◽  
Thomas M. Smith ◽  
Richard W. Reynolds
Keyword(s):  
Indian Ocean ◽  
North Atlantic ◽  
North Pacific ◽  
Tropical Indian Ocean ◽  
South Atlantic ◽  
Equatorial Pacific ◽  
The South ◽  
The North ◽  
Eastern Equatorial Pacific ◽  
Interdecadal Changes

Abstract SST predictions are usually issued in terms of anomalies and standardized anomalies relative to a 30-yr normal: climatological mean (CM) and standard deviation (SD). The World Meteorological Organization (WMO) suggests updating the 30-yr normal every 10 yr. In complying with the WMO's suggestion, a new 30-yr normal for the 1971–2000 base period is constructed. To put the new 30-yr normal in historical perspective, all the 30-yr normals since 1871 are investigated, starting from the beginning of each decade (1871–1900, 1881–1910, … , 1971–2000). Using the extended reconstructed sea surface temperature (ERSST) on a 2° grid for 1854–2000 and the Hadley Centre Sea Ice and SST dataset (HadISST) on a 1° grid for 1870–1999, eleven 30-yr normals are calculated, and the interdecadal changes of seasonal CM, seasonal SD, and seasonal persistence (P) are discussed. The interdecadal changes of seasonal CM are prominent (0.3°–0.6°) in the tropical Indian Ocean, the midlatitude North Pacific, the midlatitude North Atlantic, most of the South Atlantic, and the sub-Antarctic front. Four SST indices are used to represent the key regions of the interdecadal changes: the Indian Ocean (“INDIAN”; 10°S–25°N, 45°–100°E), the Pacific decadal oscillation (PDO; 35°–45°N, 160°E–160°W), the North Atlantic Oscillation (NAO; 40°–60°N, 20°–60°W), and the South Atlantic (SATL; 22°S–2°N, 35°W–10°E). Both INDIAN and SATL show a warming trend that is consistent between ERSST and HadISST. Both PDO and NAO show a multidecadal oscillation that is consistent between ERSST and HadISST except that HadISST is biased toward warm in summer and cold in winter relative to ERSST. The interdecadal changes in Niño-3 (5°S–5°N, 90°–150°W) are small (0.2°) and are inconsistent between ERSST and HadISST. The seasonal SD is prominent in the eastern equatorial Pacific, the North Pacific, and North Atlantic. The seasonal SD in Niño-3 varies interdecadally: intermediate during 1885–1910, small during 1910–65, and large during 1965–2000. These interdecadal changes of ENSO variance are further verified by the Darwin sea level pressure. The seasonality of ENSO variance (smallest in spring and largest in winter) also varies interdecadally: moderate during 1885–1910, weak during 1910–65, and strong during 1965–2000. The interdecadal changes of the seasonal SD of other indices are weak and cannot be determined well by the datasets. The seasonal P, measured by the autocorrelation of seasonal anomalies at a two-season lag, is largest in the eastern equatorial Pacific, the tropical Indian, and the tropical North and South Atlantic Oceans. It is also seasonally dependent. The “spring barrier” of P in Niño-3 (largest in summer and smallest in winter) varies interdecadally: relatively weak during 1885–1910, moderate during 1910–55, strong during 1955–75, and moderate during 1975–2000. The interdecadal changes of SD and P not only have important implications for SST forecasts but also have significant scientific values to be explored.

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