scholarly journals Impact of decadal reversals of the north Ionian circulation on phytoplankton phenology

2018 ◽  
Vol 15 (14) ◽  
pp. 4431-4445 ◽  
Author(s):  
Héloise Lavigne ◽  
Giuseppe Civitarese ◽  
Miroslav Gačić ◽  
Fabrizio D'Ortenzio
Keyword(s):  
Surface Waters ◽  
Mixed Layer Depth ◽  
Late Winter ◽  
Phytoplankton Dynamics ◽  
Nutrient Distribution ◽  
The North ◽  
Circulation Regime ◽  
Circulation Patterns ◽  
Color Data ◽  
Annual Time Series

Abstract. In the north Ionian, water circulation is characterized by a decadal alternation of cyclonic and anticyclonic regime driven by the mechanism called BiOS (bimodal oscillating system). The circulation regimes affect both vertical dynamics and the nutrient distribution. The north Ionian is then a good study area to investigate how changes in circulation can affect phytoplankton dynamics in oligotrophic regions. From in situ observations, for each circulation regime the averaged distribution of isopycnals is provided, and a depth difference of about 80 m is estimated for the nitracline between the cyclonic and anticyclonic regime. Based on phytoplankton phenology metrics extracted from annual time series of satellite ocean color data for the period 1998–2012, the cyclonic and anticyclonic regimes are compared. Results show that the average chlorophyll in March, the date of bloom onset and the date of maximum chlorophyll were affected by circulation patterns in the north Ionian. In the center of the north Ionian gyre, the bloom started in December and chlorophyll was low in March when circulation was anticyclonic, whereas during the cyclonic circulation regime, a late chlorophyll peak, likely resulting from different phytoplankton dynamics, was commonly observed in March. An additional analysis shows that the winter buoyancy losses, which govern the mixed layer depth (MLD), also contribute to explaining the interannual variability in bloom onset and intensity. Two trophic regimes were then identified in the north Ionian gyre (NIG) and they could be explained with the relative position of the MLD and nitracline. The first one is characterized by an early winter bloom onset and the absence of a chlorophyll peak in March. It was observed when circulation was anticyclonic or when winter MLD was relatively shallow. Dominant regenerated production all year and an absence of significant nutrient supplies to surface waters are proposed to explain this trophic regime. Conversely, the second trophic regime is marked by a bloom onset in late winter (i.e., February) and a chlorophyll peak in March. The chlorophyll increase was interpreted as a direct response to the nutrient enrichment of surface waters. This winter–spring bloom was observed when circulation was cyclonic and when winter mixing was relatively strong.

scholarly journals Impact of decadal reversals of the North Ionian circulation on phytoplankton phenology

2017 ◽  
Author(s):  
Héloise Lavigne ◽  
Giuseppe Civitarese ◽  
Miroslav Gacic ◽  
Fabrizio D'Ortenzio
Keyword(s):  
Mixed Layer Depth ◽  
Phytoplankton Dynamics ◽  
Nutrient Distribution ◽  
The North ◽  
Circulation Regime ◽  
Circulation Patterns ◽  
Color Data ◽  
Annual Time Series ◽  
Annual Time

Abstract. In the North Ionian, water circulation is characterized by a decadal alternation of cyclonic and anticyclonic regime driven by the mechanism called BiOS (Bimodal Oscillating System). The circulation regime affects the vertical dynamics and the nutrient distribution. The North Ionian is then a good study area to investigate how changes in circulation can affect phytoplankton dynamics in oligotrophic regions. From in situ observations, for each circulation regime the averaged distribution of isopycnals is provided, and a depth difference of about 80 m is estimated for the nitracline between cyclonic and anticyclonic regime. Based on phytoplankton phenology metrics extracted from annual time-series of satellite ocean color data for the period 1998–2012, the cyclonic and anticyclonic regimes are compared. Results show that the average chlorophyll in March, the date of bloom initiation and the date of maximum chlorophyll were affected by circulation patterns in the North Ionian. In the center of the gyre, bloom initiation occurred in December and chlorophyll was low in March when circulation was anticyclonic, whereas during the cyclonic circulation regime, a late chlorophyll peak, likely resulting from different phytoplankton dynamics, was commonly observed in March. An additional analysis shows that the winter buoyancy losses, which govern the Mixed Layer Depth (MLD) also contribute to explain the interannual variability in bloom initiation and intensity. Two scenarios involving the relative position of the MLD and nitracline are finally developed, discussed and tested with model data to explain the different phenology patterns observed in the North Ionian.

scholarly journals Sub meso scale phytoplankton distribution in the North East Atlantic surface waters determined with an automated flow cytometer

2009 ◽  
Vol 6 (4) ◽  
pp. 569-583 ◽  
Author(s):  
M. Thyssen ◽  
N. Garcia ◽  
M. Denis
Keyword(s):  
Surface Waters ◽  
High Frequency ◽  
Mixed Layer Depth ◽  
Nutrient Concentrations ◽  
Layer Depth ◽  
East Atlantic ◽  
North East ◽  
The North ◽  
Phytoplankton Distribution ◽  
Meso Scale

Abstract. Phytoplankton cells in the size range ~1–50 μm were analysed in surface waters using an automated flow cytometer, the Cytosub (http://www.cytobuoy.com), from the Azores to the French Brittany during spring 2007. The Cytosub records the pulse shape of the optical signals generated by phytoplankton cells when intercepted by the laser beam. A total of 6 distinct optical groups were resolved during the whole transect, and the high frequency sampling (15 min) provided evidence for the cellular cycle (based on cyclic changes in cell size and fluorescence) and distribution changes linked to the different water characteristics crossed in the North East Atlantic provinces. Nutrient concentrations and mixed layer depth varied from west to east, with a decrease in the mixed layer depth and high nutrient concentrations in the middle of the transect as well as near the French coast. Data provided a link between the sub meso scale processes and phytoplankton patchiness, some abundance variations due to the cellular cycle can be pointed out. The high frequency spatial sampling encompasses temporal variations of the phytoplankton abundance, offering a better insight into phytoplankton distribution.

scholarly journals Sub meso scale phytoplankton distribution in the north east Atlantic surface waters determined with an automated flow cytometer

2008 ◽  
Vol 5 (3) ◽  
pp. 2471-2503
Author(s):  
M. Thyssen ◽  
N. Garcia ◽  
M. Denis
Keyword(s):  
Surface Waters ◽  
High Frequency ◽  
Mixed Layer Depth ◽  
Nutrient Concentrations ◽  
Layer Depth ◽  
East Atlantic ◽  
North East ◽  
The North ◽  
Phytoplankton Distribution ◽  
Meso Scale

Abstract. Phytoplankton cells in the size range ~1–50 μm were analysed in surface waters using an automated flow cytometer, the Cytosub (http://www.cytobuoy.com), from the Azores to the French Brittany during spring 2007. The Cytosub records the pulse shape of the optical signals generated by phytoplankton cells when intercepted by the laser beam. A total of 6 distinct optical groups were resolved during the whole transect, and the high frequency sampling (15 min) provided evidence for the cellular cycle (based on cyclic changes in cell size and fluorescence) and distribution changes linked to the different water characteristics crossed in the north east Atlantic provinces. Nutrient concentrations and mixed layer depth varied from west to east, with a decrease in the mixed layer depth and high nutrient concentrations in the middle of the transect as well as near the French coast. Data provided a link between the sub meso scale processes and phytoplankton patchiness, some abundance variations due to the cellular cycle can be pointed out. The high frequency spatial sampling encompasses temporal variations of the phytoplankton abundance, offering a better insight into phytoplankton distribution.

scholarly journals Decadal Variability in the Formation of the North Pacific Subtropical Mode Water: Oceanic versus Atmospheric Control

2006 ◽  
Vol 36 (7) ◽  
pp. 1365-1380 ◽  
Author(s):  
Bo Qiu ◽  
Shuiming Chen
Keyword(s):  
Mixed Layer ◽  
Mixed Layer Depth ◽  
Dynamic State ◽  
Late Winter ◽  
Layer Depth ◽  
Mode Water ◽  
The North ◽  
Winter Mixed Layer ◽  
Recirculation Gyre ◽  
The North Pacific

Abstract In situ temperature and altimetrically derived sea surface height data are used to investigate the low-frequency variations in the formation of the North Pacific Ocean Subtropical Mode Water (STMW) over the past 12 yr. Inside the Kuroshio Extension (KE) recirculation gyre where STMW forms, the dominant signal is characterized by a gradual thinning in the late winter mixed layer depth and in the 16°–18°C thermostad layer from 1993 to 1999 and a subsequent steady thickening of these features after 2000. This same decadal signal is also seen in the low-potential-vorticity (PV) STMW layer in the interior subtropical gyre south of the recirculation gyre. By analyzing the air–sea flux data from the NCEP–NCAR reanalysis project, little correlation is found between the decadal STMW signal and the year-to-year changes in the cumulative wintertime surface cooling. In contrast, the decadal signal is found to be closely related to variability in the dynamic state of the KE system. Specifically, STMW formation is reduced when the KE path is in a variable state, during which time high regional eddy variability infuses high-PV KE water into the recirculation gyre, increasing the upper-ocean stratification and hindering the development of a deep winter mixed layer. A stable KE path, on the other hand, favors the maintenance of a weak stratification, leading to a deep winter mixed layer and formation of a thick STMW layer. The relative importance of the surface air–sea flux forcing versus the preconditioning stratification in controlling the variations in the late winter mixed layer depth is quantified using both a simple upper-ocean heat conservation model and a bulk mixed layer model. The majority of the variance (∼80%) is found to be due to the stratification changes controlled by the dynamic state of the KE system.

scholarly journals Space-Time Sea Surface pCO2 Estimation in the North Atlantic Based on CatBoost

2021 ◽  
Vol 13 (14) ◽  
pp. 2805
Author(s):  
Hongwei Sun ◽  
Junyu He ◽  
Yihui Chen ◽  
Boyu Zhao
Keyword(s):  
North Atlantic ◽  
Function Analysis ◽  
Biological Activities ◽  
Mixed Layer Depth ◽  
Sea Surface ◽  
Coefficient Of Determination ◽  
Mean Bias Error ◽  
Bias Error ◽  
The North ◽  
The North Atlantic

Sea surface partial pressure of CO2 (pCO2) is a critical parameter in the quantification of air–sea CO2 flux, which plays an important role in calculating the global carbon budget and ocean acidification. In this study, we used chlorophyll-a concentration (Chla), sea surface temperature (SST), dissolved and particulate detrital matter absorption coefficient (Adg), the diffuse attenuation coefficient of downwelling irradiance at 490 nm (Kd) and mixed layer depth (MLD) as input data for retrieving the sea surface pCO2 in the North Atlantic based on a remote sensing empirical approach with the Categorical Boosting (CatBoost) algorithm. The results showed that the root mean square error (RMSE) is 8.25 μatm, the mean bias error (MAE) is 4.92 μatm and the coefficient of determination (R2) can reach 0.946 in the validation set. Subsequently, the proposed algorithm was applied to the sea surface pCO2 in the North Atlantic Ocean during 2003–2020. It can be found that the North Atlantic sea surface pCO2 has a clear trend with latitude variations and have strong seasonal changes. Furthermore, through variance analysis and EOF (empirical orthogonal function) analysis, the sea surface pCO2 in this area is mainly affected by sea temperature and salinity, while it can also be influenced by biological activities in some sub-regions.

Phthalate Esters and Other Industrial Organic Chemicals in the North and Irish Seas

1991 ◽  
Vol 24 (10) ◽  
pp. 127-134 ◽  
Author(s):  
R. J. Law ◽  
T. W. Fileman ◽  
P. Matthiessen
Keyword(s):  
Surface Waters ◽  
Phthalate Esters ◽  
Organic Chemicals ◽  
Ion Detection ◽  
Ecotoxicological Assessment ◽  
Industrial Activities ◽  
The North ◽  
Detection Mode

Concentrations of a range of industrial organic chemicals (xylene, styrene, chlorobenzene and five phthalate esters) have been determined in surface waters near the Humber, Mersey, Tamar, Tees and Tyne estuaries. Analyses were conducted using GC/MS in the multiple ion detection mode. In general, the highest concentrations (in the ng to µg dm−3 range) for all determinands were found at sites within the estuaries. Selected samples were also analysed by scanning GC/MS and other compounds tentatively identified. There was only minor overlap between the compounds found at each of the estuaries, presumably a reflection of the industrial activities in the area. A preliminary ecotoxicological assessment was made of both datasets.

scholarly journals The Arctic vortex in March 2011: a dynamical perspective

2011 ◽  
Vol 11 (22) ◽  
pp. 11447-11453 ◽  
Author(s):  
M. M. Hurwitz ◽  
P. A. Newman ◽  
C. I. Garfinkel
Keyword(s):  
Planetary Wave ◽  
La Niña ◽  
The Arctic ◽  
Late Winter ◽  
Quasi Biennial Oscillation ◽  
The North ◽  
La Nina ◽  
Sea Surface Temperature Anomalies ◽  
Biennial Oscillation ◽  
The North Pacific

Abstract. Despite the record ozone loss observed in March 2011, dynamical conditions in the Arctic stratosphere were unusual but not unprecedented. Weak planetary wave driving in February preceded cold anomalies in the polar lower stratosphere in March and a relatively late breakup of the Arctic vortex in April. La Niña conditions and the westerly phase of the quasi-biennial oscillation (QBO) were observed in March 2011. Though these conditions are generally associated with a stronger vortex in mid-winter, the respective cold anomalies do not persist through March. Therefore, the La Niña and QBO-westerly conditions cannot explain the observed cold anomalies in March 2011. In contrast, positive sea surface temperature anomalies in the North Pacific may have contributed to the unusually weak tropospheric wave driving and strong Arctic vortex in late winter 2011.

scholarly journals Sea-surface CO<sub>2</sub> fugacity in the subpolar North Atlantic

2008 ◽  
Vol 5 (2) ◽  
pp. 535-547 ◽  
Author(s):  
A. Olsen ◽  
K. R. Brown ◽  
M. Chierici ◽  
T. Johannessen ◽  
C. Neill
Keyword(s):  
North Atlantic ◽  
Surface Waters ◽  
Mixed Layer Depth ◽  
Sea Surface ◽  
First Year ◽  
Layer Depth ◽  
High Resolution Data ◽  
Chl A ◽  
Wide Range ◽  
Summer Warming

Abstract. We present the first year-long subpolar trans-Atlantic set of surface seawater CO2 fugacity (fCO2sw) data. The data were obtained aboard the MV Nuka Arctica in 2005 and provide a quasi-continuous picture of the fCO2sw variability between Denmark and Greenland. Complementary real-time high-resolution data of surface chlorophyll-a (chl-a) concentrations and mixed layer depth (MLD) estimates have been collocated with the fCO2sw data. Off-shelf fCO2sw data exhibit a pronounced seasonal cycle. In winter, surface waters are saturated to slightly supersaturated over a wide range of temperatures. Through spring and summer, fCO2sw decreases by approximately 60 μatm, due to biological carbon consumption, which is not fully counteracted by the fCO2sw increase due to summer warming. The changes are synchronous with changes in chl-a concentrations and MLD, both of which are exponentially correlated with fCO2sw in off-shelf regions.

scholarly journals The circulation of the surface waters of the North Atlantic Ocean

1900 ◽  
Vol 66 (424-433) ◽  
pp. 484-485
Keyword(s):  
Atlantic Ocean ◽  
North Atlantic ◽  
Surface Waters ◽  
North Atlantic Ocean ◽  
The North ◽  
The North Atlantic

In this paper an attempt is made to investigate the normal circulation of the surface waters of the Atlantic Ocean north of 40° N. lat., and its changes, by means of a series of synoptic charts showing the distribution of temperature and salinity over the area for each month of the two years 1896 and 1897.

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