scholarly journals A Time History of Pre- and Post-Bomb Radiocarbon in the Barents Sea Derived from Arcto-Norwegian Cod Otoliths

Radiocarbon ◽  
2001 ◽  
Vol 43 (2B) ◽  
pp. 843-855 ◽  
Author(s):  
John M Kalish ◽  
Reidar Nydal ◽  
Kjell H Nedreaas ◽  
George S Burr ◽  
Gro L Eine
Keyword(s):  
Time Series ◽  
Ocean Circulation ◽  
General Circulation ◽  
Barents Sea ◽  
Dissolved Inorganic Carbon ◽  
Time History ◽  
General Circulation Models ◽  
Fine Tuning ◽  
Birth Date ◽  
The Barents Sea

Radiocarbon measured in seawater dissolved inorganic carbon (DIC) can be used to investigate ocean circulation, atmosphere/ocean carbon flux, and provide powerful constraints for the fine-tuning of general circulation models (GCMs). Time series of 14C in seawater are derived most frequently from annual bands of hermatypic corals. However, this proxy is unavailable in temperate and polar oceans. Fish otoliths, calcium carbonate auditory, and gravity receptors in the membranous labyrinths of teleost fishes, can act as proxies for 14C in most oceans and at most depths. Arcto-Norwegian cod otoliths are suited to this application due to the well-defined distribution of this species in the Barents Sea, the ability to determine ages of individual Arcto-Norwegian cod with a high level of accuracy, and the availability of archived otoliths collected for fisheries research over the past 60 years. Using measurements of 14C derived from Arcto-Norwegian cod otoliths, we present the first pre- and post-bomb time series (1919–1992) of 14C from polar seas and consider the significance of these data in relation to ocean circulation and atmosphere/ocean flux of 14C. The data provide evidence for a minor Suess effect of only 0.2‰ per year between 1919 and 1950. Bomb 14C was evident in the Barents Sea as early as 1957 and the highest 14C value was measured in an otolith core from a cod with a birth date of 1967. The otolith 14C data display key features common to records of 14C obtained from a Georges Bank mollusc and corals from the tropical and subtropical North Atlantic.

Chapter 22 Modern glaciers and climate change

1997 ◽  
Vol 17 (1) ◽  
pp. 436-448
Author(s):  
Julian A. Dowdeswell ◽  
Evelyn K. Dowdeswell
Keyword(s):  
Ocean Circulation ◽  
General Circulation ◽  
Barents Sea ◽  
General Circulation Models ◽  
High Arctic ◽  
Ice Age ◽  
Svalbard Archipelago ◽  
Air Masses ◽  
Ice Caps ◽  
Novaya Zemlya

By the start of the Holocene, the decay of the large ice sheet over Svalbard and the Barents Sea region was nearing completion, and glacier ice was approaching its present distribution (Elverhøi et al. 1993; Siegert & Dowdeswell 1995). Throughout most of the last 10 000 years, the extent of glaciers and ice caps over the archipelago has been no greater than that observed today, with the exception of minor readvances in the relatively cold 'Little Ice Age', which terminated at the beginning of the twentieth century. Nonetheless, ice today covers about 62% of the 62 000 km2 Svalbard archipelago (Fig. 22.1).Svalbard is one of four heavily ice-covered archipelagos in the Eurasian High Arctic; those to the east are Russian Franz Josef Land, Severnaya Zemlya and Novaya Zemlya. The ice cover on each archipelago is a function of topography and the location of each along the strong west-east gradient in climate across the Eurasian Arctic. Svalbard, as the most westerly of the four, is the warmest and receives the highest precipitation. This is due to its proximity to the relatively warm oceanic North Atlantic Drift and to the depression tracks transferring relatively temperate, moist air masses northward through the Norwegian-Greenland Sea. This position at the northernmost limit of both warm water and air masses makes the archipelago and its glaciers very sensitive to changes in atmospheric and ocean circulation. In addition, General Circulation Models (GCMs) predict that any future C02-induced warming will be most significant at high northern latitudes

MITIGATION OF TIME SERIES APPROACH ON CLIMATE CHANGE ADAPTATION ON RAINFALL OF WADI AL-AQIQ, MADINAH, SAUDI ARABIA

2017 ◽  
Vol 79 (5) ◽  
Author(s):  
Norhan Abd Rahman ◽  
Zulkifli Yusop ◽  
Zekai Şen ◽  
Saud Taher ◽  
Ibrahim Lawal Kane
Keyword(s):  
Climate Change ◽  
Time Series ◽  
Saudi Arabia ◽  
State Space ◽  
General Circulation ◽  
Temporal Dynamics ◽  
Resource Planning ◽  
General Circulation Models ◽  
Trend Test ◽  
Fluctuation Analysis

Rainfall record plays a significant role in assessment of climate change, water resource planning and management. In arid region, studies on rainfall are rather scarce due to intricacy and constraint of the available data. Most available studies use more advanced approaches such as A2 scenario, General Circulation Models (GCM) and the like, to study the temporal dynamics and make projection on future rainfall. However, those models take no account of the data patterns and its predictability. Therefore, this study uses time series analysis methodologies such as Mann- Kendall trend test, de-trended fluctuation analysis and state space time series approaches to study the dynamics of rainfall records of four stations in and around Wadi Al-Aqiq, Kingdom of Saudi Arabia (KSA). According to Mann-Kendall trend test there are decreasing trend in three out of the four stations. The de-trended fluctuation analysis revealed two distinct scaling properties that spells the predictability of the records and confirmed by state space methods. 

Transient Tracers and Anthropogenic Carbon in Central Labrador Sea: a Multi-Decadal Study

2020 ◽  
Author(s):  
Lorenza Raimondi ◽  
Kumiko Azetsu-Scott ◽  
Toste Tanhua ◽  
Igor Yashayaev ◽  
Doug Wallace
Keyword(s):  
Time Series ◽  
Temporal Variability ◽  
Dissolved Inorganic Carbon ◽  
Mixed Layer Depth ◽  
Monitoring Program ◽  
Time History ◽  
Labrador Sea ◽  
Full Time ◽  
Time Varying ◽  
Anthropogenic Carbon

<p>Over the last thirty years the Bedford Institute of Oceanography (BIO) has been maintaining the Atlantic Zone Off-Shore Monitoring Program (AZOMP), which includes annual occupation of several sections and stations in the Northwest Atlantic Ocean. Among these, the AR7W line across the Labrador Sea has one of the longest time-series where both transient tracers and dissolved inorganic carbon (DIC) have been collected since the early 1990s.</p><p>Among multiple transient tracers that have been measured along this transect (CFC-11, CFC-113, CCl<sub>4</sub> and SF<sub>6</sub>), only measurement of CFC-12 extends over the full time-series from 1992 to 2018, overlapping with DIC observations. Measurements of CFC-12 were also available for a previous cruise in 1986, extending the time-series to three decades.</p><p>In this work we present the temporal variability of CFC-12 (1986-2016) and DIC (1992-2016) concentrations as well as their distribution in the major water masses of the region.</p><p>The CFC-12 data are used to reconstruct the time-history of the tracer’s saturation at the time of convection based on multiple regression with the atmospheric input function of CFC-12 and the annual maximum mixed layer depth. The so-modelled time-varying saturation is employed to relax the constant saturation assumption of the Transit Time Distribution (TTD) method, allowing for a better estimate of anthropogenic carbon (C<sub>ant</sub>) in the region.</p><p>We present the column inventories and storage rate of C<sub>ant</sub> in central Labrador Sea between 1986 and 2016 obtained using the TTD method with time-varying saturation. We compare these estimates with a classical TTD approach that assumes constant saturation, and we highlight the differences in trends and magnitudes obtained with the two approaches.    </p><p>Finally, our work shows the multi-decadal dataset of DIC in the Labrador Sea which enables a comparison between the TTD-based C<sub>ant</sub> estimates and the measured DIC trends, providing insights into temporal variability of natural carbon in the region.</p>

scholarly journals Preformed and regenerated phosphate in ocean general circulation models: can right total concentrations be wrong?

2012 ◽  
Vol 9 (5) ◽  
pp. 1797-1807 ◽  
Author(s):  
O. Duteil ◽  
W. Koeve ◽  
A. Oschlies ◽  
O. Aumont ◽  
D. Bianchi ◽  
...  
Keyword(s):  
Ocean Circulation ◽  
General Circulation ◽  
General Circulation Models ◽  
Global Ocean ◽  
Volume Distribution ◽  
Total Phosphate ◽  
Biogeochemical Models ◽  
Ocean General Circulation Models ◽  
Carbon Pump ◽  
Biological Carbon Pump

Abstract. Phosphate distributions simulated by seven state-of-the-art biogeochemical ocean circulation models are evaluated against observations of global ocean nutrient distributions. The biogeochemical models exhibit different structural complexities, ranging from simple nutrient-restoring to multi-nutrient NPZD type models. We evaluate the simulations using the observed volume distribution of phosphate. The errors in these simulated volume class distributions are significantly larger when preformed phosphate (or regenerated phosphate) rather than total phosphate is considered. Our analysis reveals that models can achieve similarly good fits to observed total phosphate distributions for a~very different partitioning into preformed and regenerated nutrient components. This has implications for the strength and potential climate sensitivity of the simulated biological carbon pump. We suggest complementing the use of total nutrient distributions for assessing model skill by an evaluation of the respective preformed and regenerated nutrient components.

scholarly journals ENSO's non-stationary and non-Gaussian character: the role of climate shifts

2009 ◽  
Vol 16 (4) ◽  
pp. 453-473 ◽  
Author(s):  
J. Boucharel ◽  
B. Dewitte ◽  
B. Garel ◽  
Y. du Penhoat
Keyword(s):  
Time Series ◽  
General Circulation ◽  
Southern Oscillation ◽  
General Circulation Models ◽  
Coupled Models ◽  
Intergovernmental Panel ◽  
Climate Shifts ◽  
Nonlinear Advection ◽  
Non Gaussian ◽  
Mean State

Abstract. El Niño Southern Oscillation (ENSO) is the dominant mode of climate variability in the Pacific, having socio-economic impacts on surrounding regions. ENSO exhibits significant modulation on decadal to inter-decadal time scales which is related to changes in its characteristics (onset, amplitude, frequency, propagation, and predictability). Some of these characteristics tend to be overlooked in ENSO studies, such as its asymmetry (the number and amplitude of warm and cold events are not equal) and the deviation of its statistics from those of the Gaussian distribution. These properties could be related to the ability of the current generation of coupled models to predict ENSO and its modulation. Here, ENSO's non-Gaussian nature and asymmetry are diagnosed from in situ data and a variety of models (from intermediate complexity models to full-physics coupled general circulation models (CGCMs)) using robust statistical tools initially designed for financial mathematics studies. In particular α-stable laws are used as theoretical background material to measure (and quantify) the non-Gaussian character of ENSO time series and to estimate the skill of ``naïve'' statistical models in producing deviation from Gaussian laws and asymmetry. The former are based on non-stationary processes dominated by abrupt changes in mean state and empirical variance. It is shown that the α-stable character of ENSO may result from the presence of climate shifts in the time series. Also, cool (warm) periods are associated with ENSO statistics having a stronger (weaker) tendency towards Gaussianity and lower (greater) asymmetry. This supports the hypothesis of ENSO being rectified by changes in mean state through nonlinear processes. The relationship between changes in mean state and nonlinearity (skewness) is further investigated both in the Zebiak and Cane (1987)'s model and the models of the Intergovernmental Panel for Climate Change (IPCC). Whereas there is a clear relationship in all models between ENSO asymmetry (as measured by skewness or nonlinear advection) and changes in mean state, they exhibit a variety of behaviour with regard to α-stability. This suggests that the dynamics associated with climate shifts and the occurrence of extreme events involve higher-order statistical moments that cannot be accounted for solely by nonlinear advection.

Assessment of future heat events for the city of Augsburg by means of a normal vector based analog approach

2020 ◽  
Author(s):  
Christian Merkenschlager ◽  
Christoph Beck ◽  
Elke Hertig
Keyword(s):  
Time Series ◽  
Urban Areas ◽  
General Circulation ◽  
Heat Waves ◽  
Selection Process ◽  
General Circulation Models ◽  
Normal Vector ◽  
Urban Structure ◽  
Data Set ◽  
The City

<p>Under enhanced anthropogenic greenhouse gas forcing heat waves are only one example of climatic risks mankind has to deal with. Especially in urban areas where most of the people will live until the end of the 21<sup>st</sup> century heat waves are a serious risk factor since the urban heat island will reinforce such events. For the city of Augsburg, new analog methods are utilized for assessing the development and impacts of heat waves taking into account the varying urban structure.</p><p>For model calibration the temperature data from the Augsburg-Mühlhausen weather station operated by the German Weather Service (DWD) and atmospheric circulation variables of the ERA5 reanalysis data set were used to analyze the recent temperature development. For this purpose, the least deviation of the normal vector was used to determine a subsample of analogs corresponding to the day of interest. The normal vector was derived from the regression plane of the prevailing circulation on the respective day. Subsequently, the temperature patterns were used to define the analog day from the subsample. For future periods, the same method was applied to model data for two representative concentration pathways (RCP4.5, RCP8.5) of different general circulation models (GCM: ACCESS1-0, CNRM-CM5, MPI-ESM-LR). Thus, we derive future time series of analogs corresponding to events prevailing in the observational period. To account for projected trends of the GCMs, the trends of all time-series were first removed and, after the analog selection process, added again according to the trends of the GCMs.</p><p>Temperature extremes are defined as days with temperatures exceeding the 90<sup>th</sup> quantile (Q90) and heat days are defined as days where at least two temperature indices (TMIN, TMEAN, TMAX) exceed Q90. When at least three consecutive days are defined as heat day a heat wave is proclaimed. Analysis have shown that under consideration of RCP8.5 (RCP4.5) and all model runs the number of heat days in the end of the 21<sup>st</sup> century will be nine (five) times higher than within the reference period 1970-2000. Furthermore, the mean duration of heatwaves will extend by factor four (two), whereby heat waves of more than 30 (15) consecutive days are possible.</p>

Variability in Southern Hemisphere Ocean Circulation from the 1980s to the 2000s

2013 ◽  
Vol 43 (9) ◽  
pp. 1981-2007 ◽  
Author(s):  
K. Katsumata ◽  
S. Masuda
Keyword(s):  
Southern Hemisphere ◽  
Ocean Circulation ◽  
General Circulation ◽  
Antarctic Circumpolar Current ◽  
General Circulation Models ◽  
Polar Front ◽  
Inverse Model ◽  
Meridional Overturning Circulation ◽  
Steady Increase ◽  
Circumpolar Current

Abstract Interannual-to-decadal variability of ocean circulation in the Southern Hemisphere was examined using data from the 1980s to the 2000s in a box inverse model to estimate transport across hydrographic sections and three ocean general circulation models (OGCMs). The westerly wind stress over the OGCM Southern Ocean showed a steady increase of 5%–8% decade−1. The meridional overturning circulation was quantified by the transport across 30°S. The OGCMs suggested a slight strengthening [from 0.2 ± 1.0 to 0.8 ± 1.3 Sv decade−1 (1 Sv ≡ 106 m3 s−1)] of the upper meridional cell (Deacon cell) and two OGCMs showed a weakening (−0.8 ± 0.6 and −1.0 ± 0.3 Sv decade−1) of the lower meridional [Antarctic Bottom Water (AABW)] cell, partly explained by contraction of the AABW volume. The box inverse estimates did not contradict these two findings. For Antarctic Circumpolar Current transport, quantified by zonal transport across four key sections, the box inverse model estimated a decrease of 5–21 Sv. Decomposition of the decrease into baroclinic transport by the Subantarctic and Polar Fronts, barotropic transport, and others shows that the decrease is mostly due to barotropic transport and transport carried by the flow north of the Subantarctic Front and south of the Polar Front. In the OGCMs, the variability of transport across key sections is often correlated with transport carried by a flow south of the Polar Front and with the southern annular mode index. In all models, then, the transport of the Antarctic Circumpolar Current, defined as the transport carried by the fronts, has not decreased significantly over the study period.

scholarly journals Feedback Mechanism Among Decadal Oscillations in Northern Hemisphere Atmospheric Circulation, Sea Ice, and Ocean Circulation

1990 ◽  
Vol 14 ◽  
pp. 120-123 ◽  
Author(s):  
M Ikeda
Keyword(s):  
Sea Ice ◽  
Atmospheric Circulation ◽  
Wind Stress ◽  
Ocean Circulation ◽  
Barents Sea ◽  
Decadal Variability ◽  
Ice Cover ◽  
Low Pressure ◽  
Feedback Mechanism ◽  
The Barents Sea

Decadal oscillations of the ice cover in the Barents Sea are examined for the period since 1950. They are highly correlated with atmospheric circulation when that circulation has an anomalous low pressure over the Barents Sea and Eurasian Basin, while the ice cover is weakly correlated with local air temperature. A feedback mechanism between Barents Sea ice and the atmospheric circulation is suggested; increased cyclonic wind-stress curl reduces cold Arctic flow to the Barents Sea and reduces the sea ice. The reduced ice cover encourages heat flux from the Barents Sea to the atmosphere, tending to reinforce the low pressure. This positive feedback amplifies the oscillations of the air–ice–ocean system driven by external forcing with relatively weak decadal variability. A two-level ocean model, which is driven by prescribed buoyancy flux and wind stresses, confirms that Arctic outflow to the Barents Sea decreases during a cyclonic wind stress.

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