Along with the mean sea level rise due to climate change, the sea level exhibits natural variations at a large number of different time scales. One of the most important is the one linked with the ...seasonal cycle. In the Northern Hemisphere winter, the sea level is as much as 20 cm below its summer values in some locations. It is customary to associate these variations with the seasonal cycle of the sea surface net heat flux which drives an upper-ocean thermal expansion creating a positive steric sea level anomaly. Here, using a novel framework based on steric sea level variance budget applied to observations and to the Estimating the Circulation and Climate of the Ocean state estimate, we demonstrate that the steric sea level seasonal cycle amplitude results from a balance between the seasonal sea surface net heat flux and the oceanic advective processes. Moreover, for up to 50% of the ocean surface, surface heat fluxes act to damp the seasonal steric sea level cycle amplitude, which is instead forced by oceanic advection processes. We also show that eddies play an important role in damping the steric sea level seasonal cycle. Our study contributes to a better understanding of the steric sea level mechanisms which is crucial to ensure accurate and reliable climate projections.
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42.
Arctic Sea Ice Reemergence Bushuk, Mitchell; Giannakis, Dimitrios; Majda, Andrew J.
Journal of climate,
07/2015, Volume:
28, Issue:
14
Journal Article
Peer reviewed
Arctic sea ice reemergence is a phenomenon in which spring sea ice anomalies are positively correlated with fall anomalies, despite a loss of correlation over the intervening summer months. This work ...employs a novel data analysis algorithm for high-dimensional multivariate datasets, coupled nonlinear Laplacian spectral analysis (NLSA), to investigate the regional and temporal aspects of this reemergence phenomenon. Coupled NLSA modes of variability of sea ice concentration (SIC), sea surface temperature (SST), and sea level pressure (SLP) are studied in the Arctic sector of a comprehensive climate model and in observations. It is found that low-dimensional families of NLSA modes are able to efficiently reproduce the prominent lagged correlation features of the raw sea ice data. In both the model and observations, these families provide an SST–sea ice reemergence mechanism, in which melt season (spring) sea ice anomalies are imprinted as SST anomalies and stored over the summer months, allowing for sea ice anomalies of the same sign to reappear in the growth season (fall). The ice anomalies of each family exhibit clear phase relationships between the Barents–Kara Seas, the Labrador Sea, and the Bering Sea, three regions that compose the majority of Arctic sea ice variability. These regional phase relationships in sea ice have a natural explanation via the SLP patterns of each family, which closely resemble the Arctic Oscillation and the Arctic dipole anomaly. These SLP patterns, along with their associated geostrophic winds and surface air temperature advection, provide a large-scale teleconnection between different regions of sea ice variability. Moreover, the SLP patterns suggest another plausible ice reemergence mechanism, via their winter-to-winter regime persistence.
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The Greenland Ice Sheet has been a major contributor to global sea-level rise in recent decades
, and it is expected to continue to be so
. Although increases in glacier flow
and surface melting
have ...been driven by oceanic
and atmospheric
warming, the magnitude and trajectory of the ice sheet's mass imbalance remain uncertain. Here we compare and combine 26 individual satellite measurements of changes in the ice sheet's volume, flow and gravitational potential to produce a reconciled estimate of its mass balance. The ice sheet was close to a state of balance in the 1990s, but annual losses have risen since then, peaking at 345 ± 66 billion tonnes per year in 2011. In all, Greenland lost 3,902 ± 342 billion tonnes of ice between 1992 and 2018, causing the mean sea level to rise by 10.8 ± 0.9 millimetres. Using three regional climate models, we show that the reduced surface mass balance has driven 1,964 ± 565 billion tonnes (50.3 per cent) of the ice loss owing to increased meltwater runoff. The remaining 1,938 ± 541 billion tonnes (49.7 per cent) of ice loss was due to increased glacier dynamical imbalance, which rose from 46 ± 37 billion tonnes per year in the 1990s to 87 ± 25 billion tonnes per year since then. The total rate of ice loss slowed to 222 ± 30 billion tonnes per year between 2013 and 2017, on average, as atmospheric circulation favoured cooler conditions
and ocean temperatures fell at the terminus of Jakobshavn Isbræ
. Cumulative ice losses from Greenland as a whole have been close to the rates predicted by the Intergovernmental Panel on Climate Change for their high-end climate warming scenario
, which forecast an additional 70 to 130 millimetres of global sea-level rise by 2100 compared with their central estimate.
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In The Gattilusio Lordships, Christopher Wright offers a window into the culturally and politically diverse world of the late medieval Aegean, through the microcosm of one of the small and ...distinctive regimes that flourished in this fragmented environment.
Recent mass loss from ice sheets and ice shelves is now persistent and prolonged enough that it impacts downstream oceanographic conditions. To demonstrate this, we use an ensemble of coupled ...GISS‐E2.1‐G simulations forced with historical estimates of anomalous freshwater, in addition to other climate forcings, from 1990 through 2019. There are detectable differences in zonal‐mean sea surface temperatures (SST) and sea ice in the Southern Ocean, and in regional sea level around Antarctica and in the western North Atlantic. These impacts mostly improve the model's representation of historical changes, including reversing the forced trends in Antarctic sea ice. The changes in SST may have implications for estimates of the SST pattern effect on climate sensitivity and for cloud feedbacks. We conclude that the changes are sufficiently large that model groups should strive to include more accurate estimates of these drivers in all‐forcing historical simulations in future coupled model intercomparisons.
Plain Language Summary
Simulations of recent historical periods are a key test of climate model reliability and skill. These model simulations require an accounting of all the drivers of climate change. We show that the impact of historical changes in freshwater fluxes from ice sheets and ice shelves on the ocean (through changes in salinity and stratification) are detectable in sea surface temperature and sea ice trends, and help improve the match between the modeled climate changes and observations. We recommend that more accurate estimates of these drivers be included in all climate simulations that do not explicitly model ice sheets and ice shelves.
Key Points
The response to anomalous meltwater from ice sheets and shelves is large enough for it to be a forcing in historical climate simulations
When the GISS model includes these drivers, Southern Ocean SST and sea ice trends better match observations
Steric and dynamic impacts on regional sea level in parts of the North Atlantic and coastal Antarctica are significant
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Drawing upon Ottoman, Russian, and Bulgarian archival sources, this book explores the nexus between the environment, epidemic disease, human mobility, and the centralizing initiatives of the Ottoman ...and Russian states in the late 18th and early 19th centuries.
As part of a broader discussion on Ottoman-Russian diplomacy, this book re-conceptualizes Ottoman-Russian relations in the Black Sea region in the 18th and 19th centuries. In response to significant increases in human mobility and the spread of epidemic diseases, Ottoman and Russian officials - at the imperial, provincial, and local levels - communicated about and coordinated their efforts to manage migratory movements and check the spread of disease in the Black Sea region. By focusing on the settlement of migrants and refugees along the peripheries of the Ottoman and Russian Empires and by foregrounding the role of local and municipal-level state authorities in the management of migration, Migration and Disease in the Black Sea Region contributes to the developing field of provincial studies in Ottoman and Russian history. This is an important book for anyone interested in comparative imperial history, migration, diaspora formation and the spread of epidemic diseases.
In this study, Assaf Yasur-Landau examines the early history of the biblical Philistines who were among the 'Sea Peoples' who migrated from the Aegean area to the Levant during the early twelfth ...century BC. Creating an archaeological narrative of the migration of the Philistines, he combines an innovative theoretical framework on the archaeology of migration with new data from excavations in Greece, Turkey, Cyprus, Syria, Lebanon, and Israel and thereby reconstructs the social history of the Aegean migration to the southern Levant. The author follows the story of the migrants from the conditions that caused the Philistines to leave their Aegean homes, to their movement eastward along the sea and land routes, to their formation of a migrant society in Philistia and their interaction with local populations in the Levant. Based on the most up-to-date evidence, this book offers a new and fresh understanding of the arrival of the Philistines in the Levant.
The Southern Ocean plays a major role in controlling the evolution of Antarctic glaciers and in turn their impact on sea level rise. We present the Southern Ocean high‐resolution (SOhi) simulation of ...the MITgcm ocean model to reproduce ice‐ocean interaction at 1/24° around Antarctica, including all ice shelf cavities and oceanic tides. We evaluate the model accuracy on the continental shelf using Marine Mammals Exploring the Oceans Pole to Pole data and compare the results with three other MITgcm ocean models (ECCO4, SOSE, and LLC4320) and the ISMIP6 temperature reconstruction. Below 400 m, all the models exhibit a warm bias on the continental shelf, but the bias is reduced in the high‐resolution simulations. We hypothesize some of the bias is due to an overestimation of sea ice cover, which reduces heat loss to the atmosphere. Both high‐resolution and accurate bathymetry are required to improve model accuracy around Antarctica.
Plain Language Summary
Warm water from the Southern Ocean melts the glaciers and ice shelves around the Antarctic margin, leading to glacier de‐stabilization, and sea level rise. We present the Southern Ocean high‐resolution (SOhi) model to better represent ocean circulation and ice‐ocean interaction around Antarctica. We assess the accuracy of SOhi with in situ data from marine mammals and compare the results with three other ocean model simulations and to a baseline reference. All model results are slightly too warm on the continental shelf, but the higher‐resolution models yield colder waters in better agreement with observations. We attribute the warm bias to an overestimation of the sea ice cover in the ocean models. An improved bathymetry also significantly improves model accuracy in Antarctica.
Key Points
High‐resolution ocean models with more complete physics are in better agreement with in situ ocean data than coarser resolution models
Accurate bathymetry is essential to capture circulation pathways and warm water intrusions on the Antarctic continental shelf
High‐resolution ocean models may remain too warm on the continental shelf because they over‐predict the sea ice cover
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49.
The first crash Dale, Richard
2004., 20140424, 2014, 2004, 2005-01-01
eBook
For nearly three centuries the spectacular rise and fall of the South Sea Company has gripped the public imagination as the most graphic warning to investors of the dangers of unbridled speculation. ...Yet history repeats itself and the same elemental forces that drove up the price of South Sea shares to dizzying heights in 1720 have in recent years produced the global crash of 1987, the Japanese stock market bubble of the 1980s/90s, and the international dot.com boom of the 1990s.
The First Crashthrows light on the current debate about investor rationality by re-examining the story of the South Sea Bubble from the standpoint of investors and commentators during and preceding the fateful Bubble year. In absorbing prose, Richard Dale describes the trading techniques of London's Exchange Alley (which included 'modern' transactions such as derivatives) and uses new data, as well as the hitherto neglected writings of a brilliant contemporary financial analyst, to show how investors lost their bearings during the Bubble period in much the same way as during the dot.com boom.
The events of 1720, as presented here, offer insights into the nature of financial markets that, being independent of place and time, deserve to be considered by today's investors everywhere. This book is therefore aimed at all those with an interest in the behavior of stock markets.
The Bering Strait oceanic heat transport influences seasonal sea ice retreat and advance in the Chukchi Sea. Monitored since 1990, it depends on water temperature and factors controlling the volume ...transport, assumed to be local winds in the strait and an oceanic pressure difference between the Pacific and Arctic oceans (the “pressure head”). Recent work suggests that variability in the pressure head, especially during summer, relates to the strength of the zonal wind in the East Siberian Sea that raises or drops sea surface height in this area via Ekman transport. We confirm that westward winds in the East Siberian Sea relate to a broader central Arctic pattern of high sea level pressure and note that anticyclonic winds over the central Arctic Ocean also favor low September sea ice extent for the Arctic as a whole by promoting ice convergence and positive temperature anomalies. Month‐to‐month persistence in the volume transport and atmospheric circulation patterns is low, but the period 1980–2017 had a significant summertime (June–August) trend toward higher sea level pressure over the central Arctic Ocean, favoring increased transports. Some recent large heat transports are associated with high water temperatures, consistent with persistence of open water in the Chukchi Sea into winter and early ice retreat in spring. The highest heat transport recorded, October 2016, resulted from high water temperatures and ideal wind conditions yielding a record‐high volume transport. November and December 2005, the only months with southward volume (and thus heat) transports, were associated with southward winds in the strait.
Plain Language Summary
The Chukchi Sea is a focus of resource exploration, and all vessels transiting the Arctic Ocean must pass through it. Sea ice conditions that affect operations in this area are influenced by month‐to‐month variations in how much oceanic heat is brought into the region from the Pacific Ocean via the Bering Strait, the narrow (~85 km wide) channel separating Russia (Chukotka) from the United States (Alaska). The oceanic heat transport depends on both the temperature of the water and volume of water that is transported. The volume transport is in part controlled by surface winds in the strait and along the East Siberian Sea coast. We show that the latter are part of a larger pattern of atmospheric circulation influencing September sea ice extent for the Arctic Ocean as a whole. We use case studies for individual months to document the varying roles on the oceanic heat transport played by water temperature, winds in the East Siberian Sea, and local winds in the Bering Strait.
Key Points
Central Arctic anticyclonic winds favor low September sea ice extent by promoting convergence, warm conditions, and a large oceanic heat flux through Bering Strait
Summertime trends toward higher Arctic Ocean sea level pressure favored increased oceanic heat transports through the Bering Strait from 1980 to 2017
Recent large Bering Strait heat transports coincide with high water temperatures, consistent with early ice retreat and late ice advance in the Chukchi Sea
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