Frontal variability and its impact on chlorophyll in the Arabian Sea

2020 ◽  
Author(s):  
Yuntao Wang ◽  
Wentao Ma ◽  
Feng Zhou ◽  
Chai Fei
Keyword(s):  
Arabian Sea ◽  
Coastal Upwelling ◽  
Cold Water ◽  
Southwest Monsoon ◽  
Ocean Dynamics ◽  
Ekman Transport ◽  
Spatial And Temporal Variability ◽  
Anomalous Field ◽  
The North ◽  
The Impact

<p>Sixteen years satellite observations are used to investigate the frontogenesis, frontal variability and its impact on chlorophyll in the Arabian Sea. Large frontal probability (FP) and high chlorophyll mainly happens near the coast, e.g., near Somalia and Oman, and its value generally decreases with offshore distance. An Empirical Orthogonal Function (EOF) is used to disentangle the spatial and temporal variability of front and chlorophyll. Prominent seasonal cycle of frontal activities is identified, peaking in summer when southwest wind prevails. The seasonality for chlorophyll is same with wind and front near Somalia, which largely impacted by monsoon. During summer, the southwest monsoon drives offshore Ekman transport and induces coastal upwelling. It transports subsurface cold water and nutrients to the surface layer, which generates fronts and enhances chlorophyll, respectively. The frontal activities can be used as an indicator to determine the chlorophyll level that high chlorophyll happens when frontal probability gets higher than 2%. At anomalous field, stronger wind can induce higher frontal activities and chlorophyll. The impact of wind on frontogenesis can extend 1,000km offshore and a simplified linear regression is applied to quantify their relationship. The variability of wind leads chlorophyll by lags increasing with distance, indicating a horizontal offshore transport of coastal water. In winter, the northeast wind is not upwelling favorable, thus the frontal activities and chlorophyll are greatly reduced off Somalia. During this period, large chlorophyll is found in the north off Oman because of mixing, thus its relationship with front is less pronounced. In the upwelling regions, fronts act as an intermedia process that connecting the wind forcing and responses of ecosystem. The frontal activities in Arabian Sea is fundamentally important to improve our understanding of monsoon related ocean dynamics.</p>

scholarly journals External forcing mechanisms controlling the North Atlantic coastal upwelling regime during the mid-Holocene

Geology ◽  
2020 ◽  
Author(s):  
Armand Hernández ◽  
Mário Cachão ◽  
Pedro Sousa ◽  
Ricardo M. Trigo ◽  
Jürg Luterbacher ◽  
...  
Keyword(s):  
North Atlantic ◽  
Coastal Upwelling ◽  
Marine Ecosystem ◽  
External Forcing ◽  
The North ◽  
New Findings ◽  
The North Atlantic ◽  
Eastern North Atlantic ◽  
Forcing Mechanisms ◽  
The Impact

Nearshore upwelling along the eastern North Atlantic margin regulates regional marine ecosystem productivity and thus impacts blue economies. While most global circulation models show an increase in the intensity and duration of seasonal upwelling at high latitudes under future human-induced warmer conditions, projections for the North Atlantic are still ambiguous. Due to the low temporal resolution of coastal upwelling records, little is known about the impact of natural forcing mechanisms on upwelling variability. Here, we present a microfossil-based proxy record and modeling simulations for the warmest period of the Holocene (ca. 9–5 ka) to estimate the contribution of the natural variability in North Atlantic upwelling via atmospheric and oceanic dynamics. We found that more frequent high-pressure conditions in the eastern North Atlantic associated with solar activity and orbital parameters triggered upwelling variations at multidecadal and millennial time scales, respectively. Our new findings offer insights into the role of external forcing mechanisms in upwelling changes before the Anthropocene, which must be considered when producing future projections of midlatitude upwelling activity.

scholarly journals Wind-driven transport of fresh shelf water into the upper 30 m of the Labrador Sea

Ocean Science ◽  
2018 ◽  
Vol 14 (5) ◽  
pp. 1247-1264 ◽  
Author(s):  
Lena M. Schulze Chretien ◽  
Eleanor Frajka-Williams
Keyword(s):  
North Atlantic ◽  
Surface Waters ◽  
Deep Convection ◽  
Greenland Ice Sheet ◽  
Ocean Model ◽  
Meridional Overturning Circulation ◽  
Ekman Transport ◽  
Labrador Sea ◽  
The North ◽  
The Impact

Abstract. The Labrador Sea is one of a small number of deep convection sites in the North Atlantic that contribute to the meridional overturning circulation. Buoyancy is lost from surface waters during winter, allowing the formation of dense deep water. During the last few decades, mass loss from the Greenland ice sheet has accelerated, releasing freshwater into the high-latitude North Atlantic. This and the enhanced Arctic freshwater export in recent years have the potential to add buoyancy to surface waters, slowing or suppressing convection in the Labrador Sea. However, the impact of freshwater on convection is dependent on whether or not it can escape the shallow, topographically trapped boundary currents encircling the Labrador Sea. Previous studies have estimated the transport of freshwater into the central Labrador Sea by focusing on the role of eddies. Here, we use a Lagrangian approach by tracking particles in a global, eddy-permitting (1/12∘) ocean model to examine where and when freshwater in the surface 30 m enters the Labrador Sea basin. We find that 60 % of the total freshwater in the top 100 m enters the basin in the top 30 m along the eastern side. The year-to-year variability in freshwater transport from the shelves to the central Labrador Sea, as found by the model trajectories in the top 30 m, is dominated by wind-driven Ekman transport rather than eddies transporting freshwater into the basin along the northeast.

COASTAL UPWELLING AT TERENGGANU AND PAHANG COASTAL WATERS: INTERACTION OF HYDROGRAPHY, CURRENT CIRCULATION AND PHYTOPLANKTON BIOMASS

2016 ◽  
Vol 78 (8) ◽  
Author(s):  
Zuraini Zainol ◽  
Mohd Fadzil Mohd Akhir
Keyword(s):  
Coastal Waters ◽  
Phytoplankton Biomass ◽  
Current Flow ◽  
Coastal Upwelling ◽  
Transition Period ◽  
Southwest Monsoon ◽  
Good Evidence ◽  
Spatial And Temporal Variability ◽  
Seasonal Influence ◽  
Current Circulation

The hydrographic characteristics and current circulation in Terengganu and Pahang coastal waters were examined for their spatial and temporal variability based on the seasonal influence during the transition period (April 2014) and southwest monsoon (June and August, 2014). The results of this study demonstrated the presence of slightly cooler water during June and August, 2014 compared to April, 2014, which indicate the existence of coastal upwelling. Furthermore, the uplifting of isotherms towards the coast during the study trip was also a good evidence of upwelling. The current flow generated by the wind was the possible reason of the features. Furthermore, this study also makes the first attempt to observe the coupling effects between coastal upwelling and the phytoplankton biomass in Terengganu and Pahang coastal waters, which is still sparse. Interestingly, apart from the nutrient availability, the coastal upwelling was believed to influence the phytoplankton biomass at the study area.

scholarly journals On the Possible Mechanisms for Saltening of the Bay of Bengal

2019 ◽  
Vol 69 (1) ◽  
pp. 93-103
Author(s):  
Anoopa Prasad C ◽  
P.V. Hareesh Kumar
Keyword(s):  
Bay Of Bengal ◽  
Arabian Sea ◽  
Coastal Upwelling ◽  
Salt Water ◽  
Dominant Role ◽  
Salinity Gradient ◽  
Ekman Transport ◽  
Surface Salinity ◽  
Near Shore ◽  
Lateral Advection

The Bay of Bengal (BoB) is a low saline basin owing to large influx of freshwater from precipitation and river runoff. To maintain the salt balance of the BoB, the incessant lowering of salinity is to be balanced by the inflow of saltier water into the basin. In the present work, various processes that contribute to the saltening of the BoB, viz. coastal upwelling, eddies and their interaction, lateral advection from Arabian Sea and tropical cyclones are discussed. In the near-shore regions, the coastal upwelling due to wind induced Ekman transport plays a dominant role in increasing the surface salinity. On the other hand, in the open ocean, the divergence induced by eddies and their mutual interaction contributes significantly to the salt water pumping. In the southern BoB, the advection from the Arabian Sea increases the salinity. The formation of cyclones in the BoB also leads to an increase in the surface salinity. However, the magnitude of saltening of the Bay due to these processes varies from north to south. The uplift of saltier water from subsurface levels increases the salinity in the surface layers thereby creating a salinity gradient and a salinity front.

Anthropogenic iron deposition alters the ecosystem and carbon balance of the Indian Ocean over a centennial timescale

2020 ◽  
Author(s):  
Anh Pham ◽  
Takamitsu Ito
Keyword(s):  
Indian Ocean ◽  
Arabian Sea ◽  
Ocean Basin ◽  
Ecosystem Dynamics ◽  
Carbon Uptake ◽  
The South ◽  
Nutrient Deposition ◽  
The North ◽  
The Indian Ocean ◽  
The Impact

<p>Phytoplankton growth in the Indian Ocean is generally limited by macronutrients (nitrogen: N and phosphorus: P) in the north and by micronutrient (iron: Fe) in the south. Increasing anthropogenic atmospheric deposition of N and dissolved Fe (dFe) into the ocean can thus lead to significant responses from marine ecosystems in this ocean basin. Previous modeling studies investigated the impacts of anthropogenic nutrient deposition on the ocean, but their results are uncertain due to incomplete representations of Fe cycling. We use a state-of-the-art ocean ecosystem and Fe cycling model to evaluate the transient responses of ocean productivity and carbon uptake in the Indian Ocean, focusing on the centennial time scale. The model incorporates all major external sources and represents a complicated internal cycling process of Fe, thus showing significant improvements in reproducing observations. Sensitivity simulations show that after a century of anthropogenic deposition, increased dFe stimulates diatoms productivity in the southern Indian Ocean poleward of 50⁰S and the southeastern tropics. Diatoms production weakens in the south of the Arabian Sea due to the P limitation, and diatoms are outcompeted there by coccolithophores and picoplankton, which have a lower P demand. These changes in diatoms and coccolithophores productions alter the balance between the organic and carbonate pumps in the Indian Ocean, increasing the carbon uptake in the south of 50⁰S and the southeastern tropics while decreasing it in the Arabian Sea. Our results reveal the important role of ecosystem dynamics in controlling the sensitivity of carbon fluxes in the Indian Ocean under the impact of anthropogenic nutrient deposition over a centennial timescale.</p>

Spatial and temporal variability of the North Korean Cold Water leading to the near-bottom cold water intrusion in Korea Strait

2004 ◽  
Vol 60 (1) ◽  
pp. 99-131 ◽  
Author(s):  
Jae-Yul Yun ◽  
Lorenz Magaard ◽  
Kuh Kim ◽  
Chang-Woong Shin ◽  
Cheolsoo Kim ◽  
...  
Keyword(s):  
Temporal Variability ◽  
Cold Water ◽  
Spatial And Temporal Variability ◽  
Korea Strait ◽  
Water Intrusion ◽  
The North ◽  
Bottom Cold Water

scholarly journals Trends in rainfall erosivity in NE Spain at annual, seasonal and daily scales, 1955–2006

2012 ◽  
Vol 9 (5) ◽  
pp. 6285-6309 ◽  
Author(s):  
M. Angulo-Martínez ◽  
S. Beguería
Keyword(s):  
Soil Degradation ◽  
Bare Soil ◽  
Western Mediterranean ◽  
Rainfall Erosivity ◽  
Spatial And Temporal Variability ◽  
Major Mechanism ◽  
The North ◽  
Mediterranean Oscillation ◽  
The Impact ◽  
Ne Spain

Abstract. Rainsplash – the detachment and transport of soil particles by the impact of raindrops on a bare soil – is a major mechanism of soil degradation and erosion on semiarid areas and agricultural lands. Rainfall erosivity refers to the ability of precipitation to erode soil, and depends on the characteristics of the raindrops – size and velocity – and on the rainfall intensity and duration. Despite the relevance of rainfall erosivity for soil degradation prevention very few studies addressed its spatial and temporal variability. On this study the time variation of rainfall erosivity in the Ebro valley (NE Spain) is assessed for the period 1955–2006. The results show a general decrease in annual and seasonal rainfall erosivity, which is explained by a decrease of very intense rainfall events whilst the frequency of moderate and low events increased. This trend is related to prevailing positive conditions of the main atmospheric teleconnection indices affecting the West Mediterranean, i.e. the North Atlantic Oscillation (NAO), the Mediterranean Oscillation (MO) and the Western Mediterranean Oscillation (WeMO).

Atmospheric summer circulation and coastal upwelling in the Arabian Sea during the Holocene and the last glaciation

1991 ◽  
Vol 36 (1) ◽  
pp. 72-93 ◽  
Author(s):  
Frank Sirocko ◽  
Michael Sarnthein ◽  
Heinz Lange ◽  
Helmut Erlenkeuser
Keyword(s):  
Arabian Sea ◽  
Coastal Upwelling ◽  
Monsoon Season ◽  
Sediment Cores ◽  
Southwest Monsoon ◽  
Accumulation Rates ◽  
Summer Circulation ◽  
The Holocene ◽  
Dust Flux ◽  
Northern Arabian Sea

AbstractAccumulation rates of biogenic and lithogenic components were studied in 39 turbidite-free, well-dated sediment cores from the northern Indian Ocean to define the proportions of fluvial and eolian input and to reconstruct Quaternary patterns of coastal upwelling. The majority of dust deposited in the western Arabian Sea during the Holocene (about 100 × 106t yr−1) is advected from Arabia by northwesterly winds, which overlie the low-level southwest monsoon. The glacial increase in dust flux to 160 × 106t yr−1 culminated in the northern Arabian Sea, most probably due to (i) entrainment of dust, rich in chlorite, dolomite, and lithogenic carbonate in the then-dry Persian Gulf, and (ii) a southward shift of the mean position of the southwest monsoon during glacial summer. This shift is recorded in reduced accumulation rates of biogenic opal and increased rates of marine carbonate off Somalia and Oman. Both the terrigenous and biogenic sediment records show that the northwesterly winds and the southwest monsoon persisted over the last 27,000 yr, as well as the Asian continental summer heat low. However, the glacial seasonal time span of the southwest monsoon season was much reduced, most likely because of a delay in the seasonal onset of the southwest monsoon.

scholarly journals The impact of upwelling on the intensification of anticyclonic ocean eddies in the Caribbean Sea

Ocean Science ◽  
2019 ◽  
Vol 15 (6) ◽  
pp. 1419-1437 ◽  
Author(s):  
Carine G. van der Boog ◽  
Julie D. Pietrzak ◽  
Henk A. Dijkstra ◽  
Nils Brüggemann ◽  
René M. van Westen ◽  
...  
Keyword(s):  
Coastal Upwelling ◽  
Caribbean Sea ◽  
Vertical Shear ◽  
Ekman Transport ◽  
Density Gradients ◽  
River Plumes ◽  
Salinity Gradients ◽  
The Caribbean ◽  
Anticyclonic Eddies ◽  
The Impact

Abstract. The mesoscale variability in the Caribbean Sea is dominated by anticyclonic eddies that are formed in the eastern part of the basin. These anticyclones intensify on their path westward while they pass the coastal upwelling region along the Venezuelan and Colombian coast. In this study, we used a regional model to show that this westward intensification of Caribbean anticyclones is steered by the advection of cold upwelling filaments. Following the thermal wind balance, the increased horizontal density gradients result in an increase in the vertical shear of the anticyclones and in their westward intensification. To assess the impact of variations in upwelling on the anticyclones, several simulations were performed in which the northward Ekman transport (and thus the upwelling strength) is altered. As expected, stronger (weaker) upwelling is associated with stronger (weaker) offshore cooling and a stronger (weaker) westward intensification of the anticyclones. Moreover, the simulations with weaker upwelling show farther advection of the Amazon and Orinoco River plumes into the basin. As a result, in these simulations the horizontal density gradients were predominantly set by horizontal salinity gradients. The importance of the horizontal density gradients driven by temperature, which are associated with the upwelling, increased with increasing upwelling strength. The results of this study highlight that both upwelling and the advection of the river plumes affect the life cycle of mesoscale eddies in the Caribbean Sea.

scholarly journals Trans-pacific transport and evolution of aerosols: Evaluation of quasi global WRF-Chem simulation with multiple observations

2016 ◽  
Author(s):  
Zhiyuan Hu ◽  
Chun Zhao ◽  
Jianping Huang ◽  
L. Ruby Leung ◽  
Yun Qian ◽  
...  
Keyword(s):  
Rural Areas ◽  
Carbonaceous Aerosol ◽  
Spatial And Temporal Variability ◽  
Marine Aerosols ◽  
Global Simulation ◽  
Model Biases ◽  
The North ◽  
Multiple Observations ◽  
The Pacific ◽  
The Impact

Abstract. A fully coupled meteorology-chemistry model (WRF-Chem) has been configured to conduct quasi-global simulation for the 5 years of 2010–2014 and evaluated with multiple observation datasets for first time. The evaluation focuses on the simulation over the trans-Pacific transport region using various reanalysis and observational datasets for meteorological fields and aerosol properties. In general, precipitation and winds are well simulated by the model. The simulation captures the overall spatial and seasonal variability of satellite retrieved aerosol optical depth (AOD) and absorbing AOD (AAOD) over the Pacific that is determined by the outflows of pollutants and dust and the emissions of marine aerosols. The assessment of simulated extinction Angstrom exponent (EAE) indicates that the model generally reproduces the variability of aerosol size distributions as seen by satellites. In addition, the vertical profile of aerosol extinction and its seasonality over the Pacific that are dominated by marine aerosols near the surface and the outflow of pollutants and dust above 4 km are also well simulated. The difference between the simulation and satellite retrievals can be mainly attributed to model biases in estimating marine aerosol emissions as well as the satellite sampling and retrieval uncertainties. Compared with the surface measurements over the western U.S., the model reproduces the observed magnitude and seasonality of dust, sulfate, and nitrate surface concentrations, but significantly underestimates the peak surface concentrations of carbonaceous aerosol likely due to model biases in the spatial and temporal variability of biomass burning emissions and secondary organic aerosol (SOA) production. A sensitivity simulation shows that the trans-Pacific transported dust, sulfate, and nitrate can make significant contribution to surface concentrations over the rural areas of the western U.S., while the peaks of carbonaceous aerosol surface concentrations are dominated by the North American emissions. Both the retrievals and simulation show small interannual variability of aerosol characteristics for 2010–2014 averaged over three Pacific sub-regions. The evaluation in this study demonstrates that the WRF-Chem quasi global simulation can be used for investigating trans-Pacific transport of aerosols and providing reasonable inflow chemical boundaries for the western U.S. to further understand the impact of transported pollutants on the regional air quality and climate with high-resolution nested regional modeling.

Sign in / Sign up

Export Citation Format

Share Document