scholarly journals Volcanic impact on the Atlantic Ocean over the last millennium

2011 ◽  
Vol 7 (4) ◽  
pp. 1439-1455 ◽  
Author(s):  
J. Mignot ◽  
M. Khodri ◽  
C. Frankignoul ◽  
J. Servonnat
Keyword(s):  
Atlantic Ocean ◽  
Radiative Forcing ◽  
Climate Models ◽  
North Atlantic Ocean ◽  
Thermal Response ◽  
Volcanic Eruptions ◽  
Total Solar Irradiance ◽  
Meridional Overturning Circulation ◽  
Oceanic Circulation ◽  
The North

Abstract. The oceanic response to volcanic eruptions over the last 1000 years is investigated with a focus on the North Atlantic Ocean, using a fully coupled AOGCM forced by a realistic time series of volcanic eruptions, total solar irradiance (TSI) and atmospheric greenhouse gases concentration. The model simulates little response to TSI variations but a strong and long-lasting thermal and dynamical oceanic adjustment to volcanic forcing, which is shown to be a function of the time period of the volcanic eruptions. The thermal response consists of a fast tropical cooling due to the radiative forcing by the volcanic eruptions, followed by a penetration of this cooling in the subtropical ocean interior one to five years after the eruption, and propagation of the anomalies toward the high latitudes. The oceanic circulation first adjusts rapidly to low latitude anomalous wind stress induced by the strong cooling. The Atlantic Meridional Overturning Circulation (AMOC) shows a significant intensification 5 to 10 years after the eruptions of the period post-1400 A.D., in response to anomalous atmospheric momentum forcing, and a slight weakening in the following decade. In response to the stronger eruptions occurring between 1100 and 1300, the AMOC shows no intensification and a stronger reduction after 10 years. This study thus stresses the diversity of AMOC response to volcanic eruptions in climate models and discusses possible explanations.

scholarly journals Volcanic impact on the Atlantic ocean over the last millennium

2011 ◽  
Vol 7 (4) ◽  
pp. 2511-2554 ◽  
Author(s):  
J. Mignot ◽  
M. Khodri ◽  
C. Frankignoul ◽  
J. Servonnat
Keyword(s):  
Atlantic Ocean ◽  
Radiative Forcing ◽  
Climate Models ◽  
North Atlantic Ocean ◽  
Thermal Response ◽  
Volcanic Eruptions ◽  
Total Solar Irradiance ◽  
Meridional Overturning Circulation ◽  
Oceanic Circulation ◽  
The North

Abstract. The oceanic response to volcanic eruptions over the last 1000 years is investigated with a focus on the North Atlantic Ocean, using a fully coupled AOGCM forced by a realistic time series of volcanic eruptions, total solar irradiance (TSI) and atmospheric greenhouse gases concentration. The model simulates little response to TSI variations but a strong and long-lasting thermal and dynamical oceanic adjustment to volcanic forcing, which is shown to be a function of the time period of the volcanic eruptions, probably due to their different seasonality. The thermal response consists of a fast tropical cooling due to the radiative forcing by the volcanic eruptions, followed by a penetration of this cooling in the subtropical ocean interior one to five years after the eruption, and propagation of the anomalies toward the high latitudes. The oceanic circulation first adjusts rapidly to low latitude anomalous wind stress induced by the strong cooling. The Atlantic Meridional Overturning Circulation (AMOC) shows a significant intensification 5 to 10 years after the eruptions of the period post-1400 AD, in response to anomalous atmospheric momentum forcing, and a slight weakening in the following decade. In response to the stronger eruptions occurring between 1100 and 1300, the AMOC shows no intensification and a stronger reduction after 10 years. This study thus stresses the diversity of AMOC response to volcanic eruptions in climate models and tentatively points to an important role of the seasonality of the eruptions.

scholarly journals NAO predictability from external forcing in the late 20th century

2021 ◽  
Vol 4 (1) ◽  
Author(s):  
Jeremy M. Klavans ◽  
Mark A. Cane ◽  
Amy C. Clement ◽  
Lisa N. Murphy
Keyword(s):  
North Atlantic ◽  
Radiative Forcing ◽  
Climate Models ◽  
North Atlantic Ocean ◽  
Signal To Noise Ratio ◽  
Prediction System ◽  
Signal To Noise ◽  
Late 20Th Century ◽  
The North ◽  
Predictive Skill

AbstractThe North Atlantic Oscillation (NAO) is predictable in climate models at near-decadal timescales. Predictive skill derives from ocean initialization, which can capture variability internal to the climate system, and from external radiative forcing. Herein, we show that predictive skill for the NAO in a very large uninitialized multi-model ensemble is commensurate with previously reported skill from a state-of-the-art initialized prediction system. The uninitialized ensemble and initialized prediction system produce similar levels of skill for northern European precipitation and North Atlantic SSTs. Identifying these predictable components becomes possible in a very large ensemble, confirming the erroneously low signal-to-noise ratio previously identified in both initialized and uninitialized climate models. Though the results here imply that external radiative forcing is a major source of predictive skill for the NAO, they also indicate that ocean initialization may be important for particular NAO events (the mid-1990s strong positive NAO), and, as previously suggested, in certain ocean regions such as the subpolar North Atlantic ocean. Overall, we suggest that improving climate models’ response to external radiative forcing may help resolve the known signal-to-noise error in climate models.

scholarly journals Investigating the impact of Lake Agassiz drainage routes on the 8.2 ka cold event with a climate model

2009 ◽  
Vol 5 (3) ◽  
pp. 471-480 ◽  
Author(s):  
Y.-X. Li ◽  
H. Renssen ◽  
A. P. Wiersma ◽  
T. E. Törnqvist
Keyword(s):  
Atlantic Ocean ◽  
North Atlantic ◽  
Climate Model ◽  
North Atlantic Ocean ◽  
Sensitivity Study ◽  
Meridional Overturning Circulation ◽  
Labrador Sea ◽  
Cold Event ◽  
The North ◽  
The Impact

Abstract. The 8.2 ka event is the most prominent abrupt climate change in the Holocene and is often believed to result from catastrophic drainage of proglacial lakes Agassiz and Ojibway (LAO) that routed through the Hudson Bay and the Labrador Sea into the North Atlantic Ocean, and perturbed Atlantic meridional overturning circulation (MOC). One key assumption of this triggering mechanism is that the LAO freshwater drainage was dispersed over the Labrador Sea. Recent data, however, show no evidence of lowered δ18O values, indicative of low salinity, from the open Labrador Sea around 8.2 ka. Instead, negative δ18O anomalies are found close to the east coast of North America, extending as far south as Cape Hatteras, North Carolina, suggesting that the freshwater drainage may have been confined to a long stretch of continental shelf before fully mixing with North Atlantic Ocean water. Here we conduct a sensitivity study that examines the effects of a southerly drainage route on the 8.2 ka event with the ECBilt-CLIO-VECODE model. Hosing experiments of four routing scenarios, where freshwater was introduced to the Labrador Sea in the northerly route and to three different locations along the southerly route, were performed to investigate the routing effects on model responses. The modeling results show that a southerly drainage route is possible but generally yields reduced climatic consequences in comparison to those of a northerly route. This finding implies that more freshwater would be required for a southerly route than for a northerly route to produce the same climate anomaly. The implicated large amount of LAO drainage for a southerly routing scenario is in line with a recent geophysical modelling study of gravitational effects on sea-level change associated with the 8.2 ka event, which suggests that the volume of drainage might be larger than previously estimated.

scholarly journals Predictability and Decadal Variability of the North Atlantic Ocean State Evaluated from a Realistic Ocean Model

2017 ◽  
Vol 30 (2) ◽  
pp. 477-498 ◽  
Author(s):  
Florian Sévellec ◽  
Alexey V. Fedorov
Keyword(s):  
Atlantic Ocean ◽  
Surface Temperature ◽  
Sea Surface Temperature ◽  
North Atlantic ◽  
Decadal Variability ◽  
North Atlantic Ocean ◽  
Meridional Overturning Circulation ◽  
Sea Surface ◽  
The North ◽  
The North Atlantic

This study investigates the excitation of decadal variability and predictability of the ocean climate state in the North Atlantic. Specifically, initial linear optimal perturbations (LOPs) in temperature and salinity that vary with depth, longitude, and latitude are computed, and the maximum impact on the ocean of these perturbations is evaluated in a realistic ocean general circulation model. The computations of the LOPs involve a maximization procedure based on Lagrange multipliers in a nonautonomous context. To assess the impact of these perturbations four different measures of the North Atlantic Ocean state are used: meridional volume and heat transports (MVT and MHT) and spatially averaged sea surface temperature (SST) and ocean heat content (OHC). It is shown that these metrics are dramatically different with regard to predictability. Whereas OHC and SST can be efficiently modified only by basin-scale anomalies, MVT and MHT are also strongly affected by smaller-scale perturbations. This suggests that instantaneous or even annual-mean values of MVT and MHT are less predictable than SST and OHC. Only when averaged over several decades do the former two metrics have predictability comparable to the latter two, which highlights the need for long-term observations of the Atlantic meridional overturning circulation in order to accumulate climatically relevant data. This study also suggests that initial errors in ocean temperature of a few millikelvins, encompassing both the upper and deep ocean, can lead to ~0.1-K errors in the predictions of North Atlantic sea surface temperature on interannual time scales. This transient error growth peaks for SST and OHC after about 6 and 10 years, respectively, implying a potential predictability barrier.

scholarly journals Modelling global-scale climate impacts of the late Miocene Messinian Salinity Crisis

2013 ◽  
Vol 9 (4) ◽  
pp. 4807-4853 ◽  
Author(s):  
R. F. Ivanovic ◽  
P. J. Valdes ◽  
R. Flecker ◽  
M. Gutjahr
Keyword(s):  
Atlantic Ocean ◽  
North Atlantic ◽  
Late Miocene ◽  
General Circulation ◽  
North Atlantic Ocean ◽  
Global Scale ◽  
Climate Impacts ◽  
Meridional Overturning Circulation ◽  
Messinian Salinity Crisis ◽  
The North

Abstract. Late Miocene tectonic changes in Mediterranean–Atlantic connectivity and climatic changes caused Mediterranean salinity to fluctuate dramatically, including a ten-fold increase and near-freshening. Recent proxy- and model-based evidence suggests that at times during this Messinian Salinity Crisis (MSC, 5.96–5.33 Ma), highly-saline and highly-fresh Mediterranean water flowed into the North Atlantic Ocean, whilst at others, no Mediterranean Outflow Water (MOW) reached the Atlantic. By running extreme, sensitivity-type experiments with a fully-coupled ocean–atmosphere general circulation model, we investigate the potential of these various MSC MOW scenarios to impact global-scale climate. The simulations suggest that MOW had a greater influence on North Atlantic Ocean circulation and climate than it does today. We also find that depending on the presence, strength and salinity of MOW, the MSC could have been capable of cooling mid-high northern latitudes by more than 1.2 °C, with the greatest cooling taking place in the Labrador, Greenland–Iceland–Norwegian and Barents Seas. With hypersaline-MOW, a component of North Atlantic Deep Water formation shifts to the Mediterranean, strengthening the Atlantic Meridional Overturning Circulation (AMOC) south of 35° N by 3–7 Sv. With hyposaline-MOW, AMOC completely shuts down, inducing a bipolar climate anomaly with strong cooling in the North (up to −10.5 °C) and weaker warming in the South (up to +2.5 °C). These simulations identify key target regions and climate variables for future proxy-reconstructions to provide the best and most robust test cases for (a) assessing Messinian model performance, (b) evaluating Mediterranean–Atlantic connectivity during the MSC and (c) establishing whether or not the MSC could ever have affected global-scale climate.

scholarly journals Temperature domination of AMOC weakening due to freshwater hosing in two GCMs

2019 ◽  
Vol 54 (1-2) ◽  
pp. 273-286 ◽  
Author(s):  
Rosalind K. Haskins ◽  
Kevin I. C. Oliver ◽  
Laura C. Jackson ◽  
Richard A. Wood ◽  
Sybren S. Drijfhout
Keyword(s):  
North Atlantic ◽  
Climate Models ◽  
North Atlantic Ocean ◽  
Global Climate ◽  
Mixed Layer Depth ◽  
Global Climate Models ◽  
Meridional Overturning Circulation ◽  
Ice Melt ◽  
The North ◽  
The North Atlantic

Abstract Anthropogenic climate change is projected to lead to a weakening of the Atlantic meridional overturning circulation (AMOC). One of the mechanisms contributing to this is ice melt leading to a freshening of the North Atlantic Ocean. We use two global climate models to investigate the role of temperature and salinity in the weakening of the AMOC resulting from freshwater forcing. This study finds that freshwater hosing reduces the strength of the AMOC, but in some situations it is not through reduced density from freshening, but a reduction in density from subsurface warming. When the freshwater is mixed down it directly reduces the density of the North Atlantic, weakening the strength of the AMOC. As the AMOC weakens, the mixed layer depth reduces and surface properties are less effectively mixed down. A buoyant surface cap forms, blocking atmospheric fluxes. This leads to the development of a warm anomaly beneath the surface cap, which becomes the primary driver of AMOC weakening. We found that the mean North Atlantic salinity anomaly can be used as a proxy for AMOC weakening because it describes the extent of this surface cap.

scholarly journals Simulated Atlantic Multidecadal Oscillation during the Holocene

2012 ◽  
Vol 25 (20) ◽  
pp. 6989-7002 ◽  
Author(s):  
Wei Wei ◽  
Gerrit Lohmann
Keyword(s):  
Atlantic Ocean ◽  
Surface Temperature ◽  
North Atlantic ◽  
North Atlantic Ocean ◽  
Atlantic Multidecadal Oscillation ◽  
Meridional Overturning Circulation ◽  
Earth System ◽  
The Holocene ◽  
The North ◽  
The North Atlantic

Abstract The Atlantic multidecadal oscillation (AMO) and its possible change during the Holocene are examined in this study, using long-term simulations of the earth system model Community Earth System Models (COSMOS). A quasi-persistent ~55–80-yr cycle characterizing in the North Atlantic sea surface temperature is highly associated with the multidecadal variability of the Atlantic meridional overturning circulation (AMOC) during the Holocene. This mode can be found throughout the Holocene, indicating that the AMO is dominated by internal climate variability. Stronger-than-normal AMOC results in warmer-than-normal surface temperature spreading over almost the whole North Hemisphere, in particular the North Atlantic Ocean. During the warm phase of the AMO, more precipitation is detected in the North Atlantic low and high latitudes. It also generates a dipolar seesaw pattern in the sea ice anomaly. The results reveal that the influence of the AMO can be amplified by a more vigorous AMOC variability during the early Holocene in the presence of a remnant of the Laurentide Ice Sheet and when freshwater entered the North Atlantic Ocean. This conclusion could have potential application for the past AMO reconstruction and the future AMO estimation.

scholarly journals Mercury distribution and transport in the North Atlantic Ocean along the GEOTRACES-GA01 transect

2018 ◽  
Vol 15 (8) ◽  
pp. 2309-2323 ◽  
Author(s):  
Daniel Cossa ◽  
Lars-Eric Heimbürger ◽  
Fiz F. Pérez ◽  
Maribel I. García-Ibáñez ◽  
Jeroen E. Sonke ◽  
...  
Keyword(s):  
Atlantic Ocean ◽  
North Atlantic ◽  
North Atlantic Ocean ◽  
Geometric Mean ◽  
Meridional Overturning Circulation ◽  
Labrador Sea ◽  
Subpolar Gyre ◽  
Data Set ◽  
The North ◽  
The North Atlantic

Abstract. We report here the results of total mercury (HgT) determinations along the 2014 Geotraces Geovide cruise (GA01 transect) in the North Atlantic Ocean (NA) from Lisbon (Portugal) to the coast of Labrador (Canada). HgT concentrations in unfiltered samples (HgTUNF) were log-normally distributed and ranged between 0.16 and 1.54 pmol L−1, with a geometric mean of 0.51 pmol L−1 for the 535 samples analysed. The dissolved fraction (< 0.45 µm) of HgT (HgTF), determined on 141 samples, averaged 78 % of the HgTUNF for the entire data set, 84 % for open seawaters (below 100 m) and 91 % if the Labrador Sea data are excluded, where the primary production was high (with a winter convection down to 1400 m). HgTUNF concentrations increased eastwards and with depth from Greenland to Europe and from subsurface to bottom waters. The HgTUNF concentrations were similarly low in the subpolar gyre waters ( ∼  0.45 pmol L−1), whereas they exceeded 0.60 pmol L−1 in the subtropical gyre waters. The HgTUNF distribution mirrored that of dissolved oxygen concentration, with highest concentration levels associated with oxygen-depleted zones. The relationship between HgTF and the apparent oxygen utilization confirms the nutrient-like behaviour of Hg in the NA. An extended optimum multiparameter analysis allowed us to characterize HgTUNF concentrations in the different source water types (SWTs) present along the transect. The distribution pattern of HgTUNF, modelled by the mixing of SWTs, show Hg enrichment in Mediterranean waters and North East Atlantic Deep Water and low concentrations in young waters formed in the subpolar gyre and Nordic seas. The change in anthropogenic Hg concentrations in the Labrador Sea Water during its eastward journey suggests a continuous decrease in Hg content in this water mass over the last decades. Calculation of the water transport driven by the Atlantic Meridional Overturning Circulation across the Portugal–Greenland transect indicates northward Hg transport within the upper limb and southward Hg transport within the lower limb, with resulting net northward transport of about 97.2 kmol yr−1.

Sign in / Sign up

Export Citation Format

Share Document