scholarly journals A comparative study of Calanus finmarchicus mortality patterns at five localities in the North Atlantic

2004 ◽  
Vol 61 (4) ◽  
pp. 687-697 ◽  
Author(s):  
M.D Ohman ◽  
K Eiane ◽  
E.G Durbin ◽  
J.A Runge ◽  
H.-J Hirche
Keyword(s):  
North Atlantic ◽  
Calanus Finmarchicus ◽  
Estimation Methods ◽  
Late Winter ◽  
Zooplankton Abundance ◽  
Biological Interactions ◽  
Georges Bank ◽  
Density Dependent ◽  
The North ◽  
The North Atlantic

Abstract We compare the patterns of stage-specific mortality of Calanus finmarchicus at five localities across the North Atlantic Ocean during the spring–summer period of active population growth: Georges Bank, a continental shelf locality in the NW Atlantic, based on 30 broadscale survey cruises in the US GLOBEC program; the northern North Sea, studied during the historic FLEX program with sampling four times daily for 73 days; Ocean Station M in the central Norwegian Sea, based on an 80-day daily time-series; and Lurefjorden (sampled weekly in late winter–early summer) and Sørfjorden (sampled monthly), two fjords in southwestern Norway characterized by markedly different guilds of predators. The mortality estimation methods included Wood's Population Surface Method, the Vertical Life Table (VLT) method, and a modified VLT, according to the study site and copepod recruitment schedules. Contrary to assumptions implicit in many simulation models and indirect methods for estimating zooplankton mortality, both rates and stage-specific patterns of mortality of C. finmarchicus vary appreciably across the North Atlantic. Characteristics of local environments, including the predator field in particular, appear to strongly influence mortality schedules in different regions. In at least two sites (Georges Bank and Ocean Station M), mortality rates of early stages of C. finmarchicus are density-dependent. We attribute this density-dependent mortality to egg cannibalism, which introduces non-linear population responses to changing environmental conditions. Region-specific biological interactions can substantially modify the effects of physical climate variability and render simple linear relationships between climate and zooplankton abundance unlikely.

Long-term ventilation changes of Subpolar Mode Waters in the North Atlantic Ocean and its impact on the oxygen distribution

2021 ◽  
Author(s):  
Ilaria Stendardo ◽  
Bruno Buongiorno Nardelli ◽  
Sara Durante
Keyword(s):  
Atlantic Ocean ◽  
North Atlantic ◽  
North Atlantic Ocean ◽  
Horizontal Resolution ◽  
Late Winter ◽  
Mode Water ◽  
Mode Waters ◽  
The North ◽  
The North Atlantic ◽  
The Impact

<p>In the subpolar North Atlantic Ocean, Subpolar Mode Waters (SPMWs) are formed during late winter convection following the cyclonic circulation of the subpolar gyre. SPMWs participate in the upper flow of the Atlantic overturning circulation (AMOC) and provide much of the water that is eventually transformed into several components of the North Atlantic deep water (NADW), the cold, deep part of the AMOC. In a warming climate, an increase in upper ocean stratification is expected to lead to a reduced ventilation and a loss of oxygen. Thus, understanding how mode waters are affected by ventilation changes will help us to better understand the variability in the AMOC. In particular, we would like to address how the volume occupied by SPMWs has varied over the last decades due to ventilation changes, and what are the aspects driving the subpolar mode water formation, their interannual variations as well as the impact of the variability in the mixing and subduction and vertical dynamics on ocean deoxygenation. For this purpose, we use two observation-based 3D products from Copernicus Marine Service (CMEMS), the ARMOR3D and the OMEGA3D datasets. The first consists of 3D temperature and salinity fields, from the surface to 1500 m depth, available weekly over a regular grid at 1/4° horizontal resolution from 1993 to present. The second consists of observation-based quasi-geostrophic vertical and horizontal ocean currents with the same temporal and spatial resolution as ARMOR3D.</p>

scholarly journals Connection between Sea Surface Anomalies and Atmospheric Quasi-Stationary Waves

2020 ◽  
Vol 33 (1) ◽  
pp. 201-212
Author(s):  
G. Wolf ◽  
A. Czaja ◽  
D. J. Brayshaw ◽  
N. P. Klingaman
Keyword(s):  
Sea Ice ◽  
North Atlantic ◽  
Southern Oscillation ◽  
Late Summer ◽  
Ice Cover ◽  
Sea Surface ◽  
Late Winter ◽  
Driving Mechanism ◽  
The North ◽  
The North Atlantic

AbstractLarge-scale, quasi-stationary atmospheric waves (QSWs) are known to be strongly connected with extreme events and general weather conditions. Yet, despite their importance, there is still a lack of understanding about what drives variability in QSW. This study is a step toward this goal, and it identifies three statistically significant connections between QSWs and sea surface anomalies (temperature and ice cover) by applying a maximum covariance analysis technique to reanalysis data (1979–2015). The two most dominant connections are linked to El Niño–Southern Oscillation and the North Atlantic Oscillation. They confirm the expected relationship between QSWs and anomalous surface conditions in the tropical Pacific and the North Atlantic, but they cannot be used to infer a driving mechanism or predictability from the sea surface temperature or the sea ice cover to the QSW. The third connection, in contrast, occurs between late winter to early spring Atlantic sea ice concentrations and anomalous QSW patterns in the following late summer to early autumn. This new finding offers a pathway for possible long-term predictability of late summer QSW occurrence.

scholarly journals Medium-term exposure of the North Atlantic copepod <i>Calanus finmarchicus</i> (Gunnerus, 1770) to CO<sub>2</sub>-acidified seawater: effects on survival and development

2013 ◽  
Vol 10 (11) ◽  
pp. 7481-7491 ◽  
Author(s):  
S. A. Pedersen ◽  
B. H. Hansen ◽  
D. Altin ◽  
A. J. Olsen
Keyword(s):  
North Atlantic ◽  
Growth And Development ◽  
Stage Iv ◽  
Subsequent Development ◽  
Experimental System ◽  
Calanus Finmarchicus ◽  
Medium Term ◽  
The North ◽  
The North Atlantic ◽  
The Impact

Abstract. The impact of medium-term exposure to CO2-acidified seawater on survival, growth and development was investigated in the North Atlantic copepod Calanus finmarchicus. Using a custom developed experimental system, fertilized eggs and subsequent development stages were exposed to normal seawater (390 ppm CO2) or one of three different levels of CO2-induced acidification (3300, 7300, 9700 ppm CO2). Following the 28-day exposure period, survival was found to be unaffected by exposure to 3300 ppm CO2, but significantly reduced at 7300 and 9700 ppm CO2. Also, the proportion of copepodite stages IV to VI observed in the different treatments was significantly affected in a manner that may indicate a CO2-induced retardation of the rate of ontogenetic development. Morphometric analysis revealed a significant increase in size (prosome length) and lipid storage volume in stage IV copepodites exposed to 3300 ppm CO2 and reduced size in stage III copepodites exposed to 7300 ppm CO2. Together, the findings indicate that a pCO2 level ≤2000 ppm (the highest CO2 level expected by the year 2300) will probably not directly affect survival in C. finmarchicus. Longer term experiments at more moderate CO2 levels are, however, necessary before the possibility that growth and development may be affected below 2000 ppm CO2 can be ruled out.

scholarly journals Modeled and Observed Multidecadal Variability in the North Atlantic Jet Stream and Its Connection to Sea Surface Temperatures

2018 ◽  
Vol 31 (20) ◽  
pp. 8313-8338 ◽  
Author(s):  
Isla R. Simpson ◽  
Clara Deser ◽  
Karen A. McKinnon ◽  
Elizabeth A. Barnes
Keyword(s):  
North Atlantic ◽  
Sea Surface ◽  
Late Winter ◽  
Jet Stream ◽  
Sea Surface Temperatures ◽  
Multidecadal Variability ◽  
The North ◽  
Surface Temperatures ◽  
The North Atlantic ◽  
North Atlantic Jet

Multidecadal variability in the North Atlantic jet stream in general circulation models (GCMs) is compared with that in reanalysis products of the twentieth century. It is found that almost all models exhibit multidecadal jet stream variability that is entirely consistent with the sampling of white noise year-to-year atmospheric fluctuations. In the observed record, the variability displays a pronounced seasonality within the winter months, with greatly enhanced variability toward the late winter. This late winter variability exceeds that found in any GCM and greatly exceeds expectations from the sampling of atmospheric noise, motivating the need for an underlying explanation. The potential roles of both external forcings and internal coupled ocean–atmosphere processes are considered. While the late winter variability is not found to be closely connected with external forcing, it is found to be strongly related to the internally generated component of Atlantic multidecadal variability (AMV) in sea surface temperatures (SSTs). In fact, consideration of the seasonality of the jet stream variability within the winter months reveals that the AMV is far more strongly connected to jet stream variability during March than the early winter months or the winter season as a whole. Reasoning is put forward for why this connection likely represents a driving of the jet stream variability by the SSTs, although the dynamics involved remain to be understood. This analysis reveals a fundamental mismatch between late winter jet stream variability in observations and GCMs and a potential source of long-term predictability of the late winter Atlantic atmospheric circulation.

scholarly journals A Nonstationary ENSO–NAO Relationship Due to AMO Modulation

2018 ◽  
Vol 32 (1) ◽  
pp. 33-43 ◽  
Author(s):  
Wenjun Zhang ◽  
Xuebin Mei ◽  
Xin Geng ◽  
Andrew G. Turner ◽  
Fei-Fei Jin
Keyword(s):  
North Atlantic ◽  
El Niño ◽  
El Nino ◽  
Southern Oscillation ◽  
Circulation Model ◽  
La Niña ◽  
Late Winter ◽  
The North ◽  
La Nina ◽  
The North Atlantic

Abstract Many previous studies have demonstrated a high uncertainty in the relationship between El Niño–Southern Oscillation (ENSO) and the North Atlantic Oscillation (NAO). In the present work, decadal modulation by the Atlantic multidecadal oscillation (AMO) is investigated as a possible cause of the nonstationary ENSO–NAO relationship based on observed and reanalysis data. It is found that the negative ENSO–NAO correlation in late winter is significant only when ENSO and the AMO are in phase (AMO+/El Niño and AMO−/La Niña). However, no significant ENSO-driven atmospheric anomalies can be observed over the North Atlantic when ENSO and the AMO are out of phase (AMO−/El Niño and AMO+/La Niña). Further analysis indicates that the sea surface temperature anomaly (SSTA) in the tropical North Atlantic (TNA) plays an essential role in this modulating effect. Because of broadly analogous TNA SSTA responses to both ENSO and the AMO during late winter, a warm SSTA in the TNA is evident when El Niño occurs during a positive AMO phase, resulting in a significantly weakened NAO, and vice versa when La Niña occurs during a negative AMO phase. In contrast, neither the TNA SSTA nor the NAO shows a prominent change under out-of-phase combinations of ENSO and AMO. The AMO modulation and the associated effect of the TNA SSTA are shown to be well reproduced by historical simulations of the HadCM3 coupled model and further verified by forced experiments using an atmospheric circulation model. These offer hope that similar models will be able to make predictions for the NAO when appropriately initialized.

Dynamics of the ENSO Teleconnection and NAO Variability in the North Atlantic–European Late Winter

2020 ◽  
Vol 33 (3) ◽  
pp. 907-923 ◽  
Author(s):  
Bianca Mezzina ◽  
Javier García-Serrano ◽  
Ileana Bladé ◽  
Fred Kucharski
Keyword(s):  
North Atlantic ◽  
Southern Oscillation ◽  
Reanalysis Data ◽  
Late Winter ◽  
Sea Level Pressure ◽  
The North ◽  
Nao Index ◽  
Eddy Heat Flux ◽  
The North Atlantic ◽  
The North Atlantic Oscillation

AbstractThe winter extratropical teleconnection of El Niño–Southern Oscillation (ENSO) in the North Atlantic–European (NAE) sector remains controversial, concerning both the amplitude of its impacts and the underlying dynamics. However, a well-established response is a late-winter (January–March) signal in sea level pressure (SLP) consisting of a dipolar pattern that resembles the North Atlantic Oscillation (NAO). Clarifying the relationship between this “NAO-like” ENSO signal and the actual NAO is the focus of this study. The ENSO–NAE teleconnection and NAO signature are diagnosed by means of linear regression onto the sea surface temperature (SST) Niño-3.4 index and an EOF-based NAO index, respectively, using long-term reanalysis data (NOAA-20CR, ERA-20CR). While the similarity in SLP is evident, the analysis of anomalous upper-tropospheric geopotential height, zonal wind, and transient-eddy momentum flux, as well as precipitation and meridional eddy heat flux, suggests that there is no dynamical link between the phenomena. The observational results are further confirmed by analyzing two 10-member ensembles of atmosphere-only simulations (using an intermediate-complexity and a state-of-the-art model) with prescribed SSTs over the twentieth century. The SST-forced variability in the Northern Hemisphere is dominated by the extratropical ENSO teleconnection, which provides modest but significant SLP skill in the NAE midlatitudes. The regional internally generated variability, estimated from residuals around the ensemble mean, corresponds to the NAO pattern. It is concluded that distinct dynamics are at play in the ENSO–NAE teleconnection and NAO variability, and caution is advised when interpreting the former in terms of the latter.

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