scholarly journals Warm-phase ENSO events modulate the continental freshwater input and the trophic state of sediments in a large South American estuary

2014 ◽  
Vol 65 (1) ◽  
pp. 1 ◽  
Author(s):  
F. García-Rodríguez ◽  
E. Brugnoli ◽  
P. Muniz ◽  
N. Venturini ◽  
L. Burone ◽  
...  
Keyword(s):  
Trophic State ◽  
Surface Sediments ◽  
River Flow ◽  
Southern Oscillation ◽  
Enso Event ◽  
South American ◽  
Freshwater Input ◽  
Enso Events ◽  
Historical Levels ◽  
Geochemical Variables

We studied the changes in geochemical variables in the middle section of Río de la Plata estuary during the 2009–2010 El Niño–Southern Oscillation (ENSO) event. Protein, organic matter, chlorophyll-a and phaeopigment content of surface sediments were significantly correlated with the increased continental freshwater input associated with high total monthly rainfall. During the warm-phase ENSO event, river flow was 5-fold larger than average historical levels, which led to a steady decrease in salinity values and the highest levels of geochemical variables. The evidence presented herein suggests that warm-phase ENSO events increase the trophic state of the sediments because of the increased freshwater input. Thus, our findings may be useful to anticipate potential eutrophication episodes in the study area.

Cultural Responses to Environmental Catastrophes: Post-El Niño Subsistence on the Prehistoric North Coast of Peru

1991 ◽  
Vol 2 (1) ◽  
pp. 27-47 ◽  
Author(s):  
Jerry D. Moore
Keyword(s):  
El Niño ◽  
El Nino ◽  
Southern Oscillation ◽  
Enso Event ◽  
North Coast ◽  
Archaeological Data ◽  
Enso Events ◽  
The North ◽  
Cultural Responses ◽  
North Coast Of Peru

Recent debate about the development of complex societies on the north coast of Peru has turned on the relative importance of marine vs. terrestrial resources and the extent to which different resource zones are upset by El Niño/Southern Oscillation (ENSO) events. While ENSO events are cited frequently as having important consequences for Prehispanic Andean societies, in fact there are few archaeological data about the nature of cultural responses to a specific ENSO event. Archaeological data from two Chimu settlements in the Casma Valley, Peru—Quebrada Sta. Cristina and Manchan—document the occurrence of a fourteenth-century A.D. ENSO event and some of the cultural responses to that prehistoric El Niño.

scholarly journals How unusual was late 20th century El Niño-Southern Oscillation (ENSO)? Assessing evidence from tree-ring, coral, ice-core and documentary palaeoarchives, A.D. 1525-2002

2006 ◽  
Vol 6 ◽  
pp. 173-179 ◽  
Author(s):  
J. L. Gergis ◽  
A. M. Fowler
Keyword(s):  
20Th Century ◽  
Tree Ring ◽  
El Niño ◽  
Large Scale ◽  
El Nino ◽  
Southern Oscillation ◽  
Enso Event ◽  
Late 20Th Century ◽  
Enso Events ◽  
Proxy Records

Abstract. Multiple proxy records (tree-ring, coral, ice and documentary) were examined to isolate ENSO signals associated with both phases of the phenomenon for the period A.D. 1525-2002. To avoid making large-scale inferences from single proxy analysis, regional signals were aggregated into a network of high-resolution records, revealing large-scale trends in the frequency, magnitude and duration of pre-instrumental ENSO using novel applications of percentile analysis. Here we use the newly introduced coupled ocean-atmosphere ENSO index (CEI) as a baseline for the calibration of proxy records. The reconstruction revealed 83 extreme or very strong ENSO episodes since A.D. 1525, expanding considerably on existing ENSO event chronologies. Significantly, excerpts of the most comprehensive list of La Niña events complied to date are presented, indicating peak activity during the 16th to mid 17th and 20th centuries. Although extreme events are seen throughout the 478-year reconstruction, 43% of the extreme ENSO events noted since A.D. 1525 occur during the 20th century, with an obvious bias towards enhanced El Niño conditions in recent decades. Of the total number of extreme event years reconstructed, 30% of all reconstructed ENSO event years occur post-1940 alone suggesting that recent ENSO variability appears anomalous in the context of the past five centuries.

Evidence of a genetic bottleneck in an El Niño affected population of South American fur seals, Arctocephalus australis

2009 ◽  
Vol 89 (8) ◽  
pp. 1717-1725 ◽  
Author(s):  
Larissa Rosa de Oliveira ◽  
Diogo Meyer ◽  
Joseph Hoffman ◽  
Patricia Majluf ◽  
João S. Morgante
Keyword(s):  
Population Size ◽  
El Niño ◽  
El Nino ◽  
Southern Oscillation ◽  
Genetic Bottleneck ◽  
South American ◽  
Enso Events ◽  
Fur Seals ◽  
The Pacific ◽  
Fur Seal

The South American fur seal, Arctocephalus australis, was one of the earliest otariid seals to be exploited by humans: at least 6000 years ago on the Atlantic coast and 4000 on the Pacific coast of South America. More than 750,000 fur seals were killed in Uruguay until 1991. However, a climatological phenomenon—the severe 1997–1998 El Niño Southern Oscillation (ENSO)—was responsible for the decline of 72% of the Peruvian fur seal population due to starvation as a consequence of warming of sea-surface temperatures and primary productivity reduction. Currently, there is no precise information on global population size or on the species' conservation status. The present study includes the first bottleneck test for the Pacific and Atlantic populations of A. australis based on the analysis of seven microsatellite loci. Genetic bottleneck compromises the evolutionary potential of a population to respond to environmental changes. The perspective becomes even more alarming due to current global warming models that predict stronger and more frequent ENSO events in the future. Our analysis found moderate support for deviation from neutrality–equilibrium for the Pacific population of fur seals and none for the Atlantic population. This difference among population reflects different demographic histories, and is consistent with a greater reduction in population size in the Pacific. Such an event could be a result of the synergic effects of recurrent ENSO events and the anthropogenic impact (sealing and prey overfishing) on this population.

scholarly journals Associating Climatic Trends with Stochastic Modelling of Flow Sequences

Geosciences ◽  
2021 ◽  
Vol 11 (6) ◽  
pp. 255
Author(s):  
Sandhya Patidar ◽  
Eleanor Tanner ◽  
Bankaru-Swamy Soundharajan ◽  
Bhaskar SenGupta
Keyword(s):  
River Flow ◽  
Hidden Markov ◽  
Southern Oscillation ◽  
Extreme Value Distribution ◽  
Stochastic Modelling ◽  
Enso Events ◽  
Climatic Trends ◽  
Modelling Framework ◽  
Highly Sensitive ◽  
Generalised Extreme Value Distribution

Water is essential to all lifeforms including various ecological, geological, hydrological, and climatic processes/activities. With the changing climate, associated El Niño/Southern Oscillation (ENSO) events appear to stimulate highly uncertain patterns of precipitation (P) and evapotranspiration (E) processes across the globe. Changes in P and EV patterns are highly sensitive to temperature (T) variation and thus also affect natural streamflow processes. This paper presents a novel suite of stochastic modelling approaches for associating streamflow sequences with climatic trends. The present work is built upon a stochastic modelling framework (HMM_GP) that integrates a hidden Markov model (HMM) with a generalised Pareto (GP) distribution for simulating synthetic flow sequences. The GP distribution within the HMM_GP model aims to improve the model’s efficiency in effectively simulating extreme events. This paper further investigated the potential of generalised extreme value distribution (GEV) coupled with an HMM model within a regression-based scheme for associating the impacts of precipitation and evapotranspiration processes on streamflow. The statistical characteristic of the pioneering modelling schematic was thoroughly assessed for its suitability to generate and predict synthetic river flow sequences for a set of future climatic projections, specifically during ENSO events. The new modelling schematic can be adapted for a range of applications in hydrology, agriculture, and climate change.

scholarly journals Influence of Pacific Meridional Mode on ENSO evolution and predictability: Asymmetric modulation and ocean preconditioning

2020 ◽  
pp. 1-61
Author(s):  
Hanjie Fan ◽  
Bohua Huang ◽  
Song Yang ◽  
Wenjie Dong
Keyword(s):  
El Niño ◽  
El Nino ◽  
Southern Oscillation ◽  
Heat Content ◽  
Enso Event ◽  
La Niña ◽  
Enso Events ◽  
La Nina ◽  
Meridional Mode ◽  
Pacific Meridional Mode

AbstractThis study investigates the mechanisms behind the Pacific Meridional Mode (PMM) in influencing the development of El Niño-Southern Oscillation (ENSO) event and its seasonal predictability. To examine the relative importance of various factors that may modulate the efficiency of the PMM influence, a series of experiments are conducted for selected ENSO events with different intensity using the Community Earth System Model, in which ensemble predictions are made from slightly different ocean initial states but under a common prescribed PMM surface heat flux forcing. Overall, the matched PMM forcing to ENSO, i.e., a positive (negative) PMM prior to an El Niño (a La Niña), plays an enhancing role, while a mismatched PMM forcing plays a damping role. For the matched cases, a positive PMM event enhances an El Niño more strongly than a negative PMM event enhances a La Niña. This asymmetry in influencing ENSO largely originates from the asymmetry in intensity between the positive and negative PMM events in the tropics, which can be explained by the nonlinearity in the growth and equatorward propagation of the PMM-related anomalies of sea surface temperature (SST) and surface zonal wind through both wind-evaporation-SST feedback and summer deep convection response. Our model results also indicate that the PMM acts as a modulator rather than a trigger for the occurrence of ENSO event. Furthermore, the response of ENSO to an imposed PMM forcing is modulated by the preconditioning of the upper-ocean heat content, which provides the memory for the coupled low-frequency evolution in the tropical Pacific.

scholarly journals Modeling the Mechanisms of Linear and Nonlinear ENSO Responses to the Pacific Meridional Mode

2016 ◽  
Vol 29 (24) ◽  
pp. 8745-8761 ◽  
Author(s):  
Erin E. Thomas ◽  
Daniel J. Vimont
Keyword(s):  
Southern Oscillation ◽  
Surface Wind ◽  
Coupled Model ◽  
Enso Event ◽  
Ocean Dynamics ◽  
Large Variability ◽  
Enso Events ◽  
The Pacific ◽  
Meridional Mode ◽  
Pacific Meridional Mode

Abstract Interactions between the Pacific meridional mode (PMM) and El Niño–Southern Oscillation (ENSO) are investigated using the National Center for Atmospheric Research (NCAR) Community Earth System Model (CESM) and an intermediate coupled model (ICM). The two models are configured so that the CESM simulates the PMM but not ENSO, and the ICM simulates ENSO but not the PMM, allowing for a clean separation between the PMM evolution and the subsequent ENSO response. An ensemble of CESM simulations is run with an imposed surface heat flux associated with the North Pacific Oscillation (NPO) generating a sea surface temperature (SST) and wind response representative of the PMM. The PMM wind is then applied as a forcing to the ICM to simulate the ENSO response. The positive (negative) ensemble-mean PMM wind forcing results in a warm (cold) ENSO event although the responses are not symmetric (warm ENSO events are larger in amplitude than cold ENSO events), and large variability between ensemble members suggests that any individual ENSO event is strongly influenced by natural variability contained within the CESM simulations. Sensitivity experiments show that 1) direct forcing of Kelvin waves by PMM winds dominates the ENSO response, 2) seasonality of PMM forcing and ENSO growth rates influences the resulting ENSO amplitude, 3) ocean dynamics within the ICM dominate the ENSO asymmetry, and 4) the nonlinear relationship between PMM wind anomalies and surface wind stress may enhance the La Niña response to negative PMM variations. Implications for ENSO variability are discussed.

Fire-climate relationships and long-lead seasonal wildfire prediction for Hawaii

2002 ◽  
Vol 11 (1) ◽  
pp. 25 ◽  
Author(s):  
Pao-Shin Chu ◽  
Weiping Yan ◽  
Francis Fujioka
Keyword(s):  
Southern Oscillation Index ◽  
Cross Validation ◽  
Southern Oscillation ◽  
Hawaiian Islands ◽  
Predictor Variable ◽  
Enso Event ◽  
Response Variable ◽  
Enso Events ◽  
Statistical Relationships ◽  
Preceding Winter

We examined statistical relationships between the seasonal Southern Oscillation Index (SOI) and total acreages burned (TAB) and the number of fires in the Hawaiian Islands. A composite of TAB during four El Niño/Southern Oscillation (ENSO) events reveals that a large total of acres burned is likely to occur from spring to summer in the year following an ENSO event. The correlation is most significant between the TAB in summer and the SOI of the antecedent winter. This relationship provides a potential for long-lead (i.e. 2 seasons in advance) prediction of wildfire activity in the Hawaiian Islands. Logistic regression is applied to predict events of large acreages burned by wildfires. The goodness of predictions is measured by specificity, sensitivity, and correctness using a cross-validation method. A comparison of prediction skill for four major islands in Hawaii is made using the summer TAB as the response variable and the preceding winter SOI as the predictor variable. For predicting the probability of events (sensitivity), results indicate rather successful skills for the islands of Oahu and Kauai, but less so for Maui and Hawaii. It is more difficult to predict non-events (specificity), with the exception of Oahu. As a result, only Oahu has a high overall correctness rate among the four islands tested.

scholarly journals Regional Variability of Surface Ocean Radiocarbon from Southern Great Barrier Reef Corals

Radiocarbon ◽  
1995 ◽  
Vol 37 (2) ◽  
pp. 517-524 ◽  
Author(s):  
Ellen R. M. Druffel ◽  
Sheila Griffin
Keyword(s):  
Dissolved Inorganic Carbon ◽  
Southern Oscillation ◽  
Enso Event ◽  
The South ◽  
Regional Variability ◽  
South Equatorial Current ◽  
Reef Corals ◽  
Surface Ocean ◽  
Enso Events ◽  
Equatorial Current

High-precision ∆14C and stable isotope (∆18O and ∆13C) records are reported for post-bomb corals from three sites off the eastern Australian coast. We observe that ∆14C values increased from ca. −50′ in the early 1950s to +130‰ by 1974, then decreased to 110‰ by 1991. There is general agreement between the coral results and ∆14C of dissolved inorganic carbon (DIC) in seawater measured previously for locations in the South Pacific. ∆14C values at our southern hemisphere sites increased at a slower rate than those observed previously in the northern hemisphere. Small variations in the ∆14C records among our three sites are likely due to differences in circulation between the shallow coastal waters and the open ocean influenced by seasonal upwelling. Low ∆14C is associated with most El Niño/Southern Oscillation (ENSO) events after 1970, indicating input of low 14C waters from the southern-shifted South Equatorial Current. The exception is the severe ENSO event of 1982–1983 when upwelling in the South Equatorial Current could have ceased, causing normal ∆14C values in the corals during this time.

scholarly journals A Pilot Study Examining U.S. Winter Cyclone Frequency Patterns Associated with Three ENSO Parameters

1998 ◽  
Vol 11 (8) ◽  
pp. 2152-2159 ◽  
Author(s):  
James Noel ◽  
David Changnon
Keyword(s):  
Pacific Northwest ◽  
El Niño ◽  
El Nino ◽  
Southern Oscillation ◽  
The United States ◽  
Enso Event ◽  
La Niña ◽  
Enso Events ◽  
La Nina ◽  
Cyclone Frequency

Abstract Teleconnections were used to link three El Niño–Southern Oscillation (ENSO) parameters to winter (December–February) cyclone frequencies over the United States during the 1949–96 period. Since each ENSO event is not exactly the same, small subsets of ENSO events were examined in addition to the more common composite ENSO event. Mean winter cyclone frequencies, derived by counting cyclones passing through 30, 5° latitude equal-area circles located in a grid from 70° to 120°W and 30° to 50°N were determined for classes of El Niños and La Niñas based on 1) the intensity of the equatorial Pacific sea surface temperature anomaly, 2) the intensity of the Tahiti–Darwin sea level pressure anomaly, and 3) the location of the 28°C isotherm. The average cyclone count for each class of El Niño and La Niña was compared to the average count for winters when no ENSO event occurred. Expected differences in cyclone frequency patterns when comparing an average of all El Niño winters to all La Niña winters were found; however, large pattern differences were also determined when comparing winters with strong El Niños to moderate–weak El Niños and similarly for La Niñas. Significant differences in number of cyclones were found in 8 of 30 circles located in the Pacific Northwest, the Great Lakes, New England, and the Southeast. The differences found in the cyclone frequency patterns for El Niños and La Niñas of different intensities and locations indicated that using a composite of all El Niños or La Niñas may provide misleading information while examination of each of these parameters independently may assist in the preparation of long-range climate predictions.

scholarly journals Linking the Pacific Meridional Mode to ENSO: Coupled Model Analysis

2009 ◽  
Vol 22 (12) ◽  
pp. 3488-3505 ◽  
Author(s):  
Li Zhang ◽  
Ping Chang ◽  
Link Ji
Keyword(s):  
Southern Oscillation ◽  
Coupled Model ◽  
Enso Event ◽  
Boreal Spring ◽  
Enso Events ◽  
Maximum Variance ◽  
Surface Circulation ◽  
The Pacific ◽  
Anomalous Surface ◽  
Thermodynamic Coupling

Abstract The occurrence of a boreal spring phenomenon referred to as the Pacific meridional model (MM) is shown to be intimately linked to the development of El Niño–Southern Oscillation (ENSO) in a long simulation of a coupled model. The MM, characterized by an anomalous north–south SST gradient and anomalous surface circulation in the northeasterly trade regime with maximum variance in boreal spring, is shown to be inherent to thermodynamic ocean–atmosphere coupling in the intertropical convergence zone (ITCZ) latitude, and the MM existence is independent of ENSO. The thermodynamic coupling enhances the persistence of the anomalous winds in the deep tropics, forcing energetic equatorially trapped oceanic waves to occur in the central western Pacific, which in turn initiate an ENSO event. The majority of ENSO events in both nature and the coupled model are preceded by MM events.

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