Modelling the sedimentary response to orbital variations. 

2021 ◽  
Author(s):  
David De Vleeschouwer ◽  
Maximilian Vahlenkamp
Keyword(s):  
North Atlantic ◽  
Middle Eocene ◽  
Planetary Science ◽  
Response Term ◽  
System Response ◽  
Carbonate Content ◽  
Boreal Winter ◽  
Winter Solstice ◽  
High Northern Latitude ◽  
Asymmetric Shape

<div> <p>Carbonate-rich middle Eocene sedimentary sequences are relatively scarce, hampering the reconstruction of paleoclimate dynamics within this high-CO<sub>2</sub> world. Nevertheless, the Newfoundland Ridge (North-Atlantic Ocean) hosts a unique sedimentary archive of middle Eocene paleoceanographic change at astronomical 10<sup>4</sup>-year resolution. International Ocean Discovery Program (IODP) Sites U1408 and U1410 exhibit well-defined lithologic alternations between calcareous ooze and clay-rich intervals, occurring at the obliquity beat and associated with changing intensities of Northern Component Water (NCW) formation (Vahlenkamp et al., 2018). These lithological variations are captured by the calcium-iron ratio (Ca/Fe) proxy as a measure of carbonate content. Yet, the asymmetric shape of the Ca/Fe cycles immediately reflects a strong non-linear response to the sinusoidal obliquity forcing. To explore the causes of this non-linearity, we built a simple physically-motivated and time-dependent model that simulates the sedimentary response at IODP Sites U1408 and U1410 between 46 and 42 million years ago.  </p> </div><div> <p>dy/dt = 1/T (b<sup>x</sup> – y)</p> </div><div> <p>The orbital input x constitutes of an insolation gradient during boreal winter (more specifically at winter solstice), as NCW formation is a high northern latitude winter process that depends on the Atlantic interhemispheric temperature gradient<span> </span>(Karas et al., 2017; Vahlenkamp et al., 2018). The latitudes between which the insolation gradient x is calculated is not user-prescribed but part of the parametrization of the model. Two further parameters define the model. The characteristic time constant T accelerates (T < 1) or slows the response to the forcing (T > 1), whereas the base of the exponential-response term b determines the degree of non-linearity in the system. We explored this four-space first with a coarse and then with a finer mesh, and found that the optimum model lies in the neighbourhood of the following values: latitudinal gradient between 63°N and 31°S, T = 4.94 kyr, b = 2.13. The corresponding system reproduces the asymmetric shape of the Ca/Fe cycles, while also exhibiting precession-obliquity interference patterns that occur in the proxy series. These kind of simple modelling efforts hold the potential to refine our mechanistic understanding of the Earth System response to astronomical forcing in the deep and warmer-than-present geologic past.</p> </div><div> <p>Karas et al. (2017) Pliocene oceanic seaways and global climate. Scientific Reports 7: 39842</p> <p>Vahlenkamp et al. (2018) Astronomically paced changes in deep-water circulation in the western North Atlantic during the middle Eocene. Earth and Planetary Science Letter 484: 329 – 340.</p> </div><p> </p><p> </p>

scholarly journals Simulated coordinated impacts of the previous autumn North Atlantic Oscillation (NAO) and winter El Niño on winter aerosol concentrations over eastern China

2019 ◽  
Vol 19 (16) ◽  
pp. 10787-10800 ◽  
Author(s):  
Juan Feng ◽  
Jianping Li ◽  
Hong Liao ◽  
Jianlei Zhu
Keyword(s):  
North Atlantic Oscillation ◽  
South China ◽  
North Atlantic ◽  
El Niño ◽  
El Nino ◽  
Eastern China ◽  
Central China ◽  
Boreal Winter ◽  
The Impact ◽  
Previous Autumn

Abstract. The high aerosol concentration (AC) over eastern China has attracted attention from both science and society. Based on the simulations of a chemical transport model using a fixed emissions level, the possible impact of the previous autumn North Atlantic Oscillation (NAO) combined with the simultaneous El Niño–Southern Oscillation (ENSO) on the boreal winter AC over eastern China is investigated. We find that the NAO only manifests its negative impacts on the AC during its negative phase over central China, and a significant positive influence on the distribution of AC is observed over south China only during the warm events of ENSO. The impact of the previous NAO on the AC occurs via an anomalous sea surface temperature tripole pattern by which a teleconnection wave train is induced that results in anomalous convergence over central China. In contrast, the occurrence of ENSO events may induce an anomalous shift in the western Pacific subtropical high and result in anomalous southwesterlies over south China. The anomalous circulations associated with a negative NAO and El Niño are not favorable for the transport of AC and correspond to worsening air conditions over central and south China. The results highlight the fact that the combined effects of tropical and extratropical systems play a considerable role in affecting the boreal winter AC over eastern China.

scholarly journals Modelling the wintertime response to upper tropospheric and lower stratospheric ozone anomalies over the North Atlantic and Europe

2003 ◽  
Vol 21 (10) ◽  
pp. 2107-2118 ◽  
Author(s):  
I. Kirchner ◽  
D. Peters
Keyword(s):  
North Atlantic ◽  
General Circulation ◽  
Initial Conditions ◽  
Stratospheric Ozone ◽  
Circulation Model ◽  
Sensitivity Study ◽  
Boreal Winter ◽  
Radiative Processes ◽  
The North ◽  
The North Atlantic

Abstract. During boreal winter months, mean longitude-dependent ozone changes in the upper troposphere and lower stratosphere are mainly caused by different ozone transport by planetary waves. The response to radiative perturbation induced by these ozone changes near the tropopause on the circulation is unclear. This response is investigated with the ECHAM4 general circulation model in a sensitivity study. In the simulation two different mean January realizations of the ozone field are implemented in ECHAM4. Both ozone fields are estimated on the basis of the observed mean January planetary wave structure of the 1980s. The first field represents a 14-year average (reference, 1979–1992) and the second one represents the mean ozone field change (anomaly, 1988–92) in boreal extra-tropics during the end of the 1980s. The model runs were carried out pairwise, with identical initial conditions for both ozone fields. Five statistically independent experiments were performed, forced with the observed sea surface temperatures for the period 1988 to 1992. The results support the hypothesis that the zonally asymmetric ozone changes of the 80s triggered a systematic alteration of the circulation over the North Atlantic – European region. It is suggested that this feedback process is important for the understanding of the decadal coupling between troposphere and stratosphere, as well as between subtropics and extra-tropics in winter.Key words. Meteorology and atmospheric dynamics (general circulation; radiative processes; synoptic-scale meteorology)

Holocene climatic and palaeoenvironmental changes in the South-Eastern Barents Sea – new insights from palaeomagnetic and geochemical stratigraphy

2020 ◽  
Author(s):  
Martin Klug ◽  
Karl Fabian ◽  
Jochen Knies ◽  
Valérie Bellec ◽  
Leif Rise
Keyword(s):  
North Atlantic ◽  
Remanent Magnetization ◽  
Late Holocene ◽  
Environmental Changes ◽  
Barents Sea ◽  
Marine Ecosystem ◽  
Planetary Science ◽  
Coastal Current ◽  
The South ◽  
South Eastern

<p>Holocene climate variability and environmental changes have been studied using a sediment record from the Barents Sea with focus on the spatio-temporal evolution of bio-productivity and terrestrial sediment deposition in response to changes of climate and regional oceanography. From a 3 m long sediment core recovered in the South-Eastern Barents Sea at 72.5°N 32.5°E u-channels were extracted and stepwise demagnetized and measured for their natural remanent magnetization (NRM) and anhysteretic remanent magnetization (ARM) at the cryogenic magnetometer facility at the Geological Survey of Norway. The u-channel measurements at 3 mm resolution allow the reconstruction of palaeoinclination, relative declination and relative palaeointensity. Comparison of these parameters to FENNOSTACK (Snowball et al., 2007) and EGLACOM-SVAIS (Sagnotti et al., 2011) establishes a robust age model for the sediment sequence which otherwise contains little datable material. We applied statistical factor analysis as centred logratio (clr) transformation to reduce dimensionality of the XRF data and compare changes in high-resolution magnetic susceptibility, wet bulk density and XRF elemental composition with changes of climate proxies in other North Atlantic sedimentary records.</p><p>Based on the new chronostratigraphic framework changes of inorganic and organic proxies at long-term and sub-millennial scale resolve the temperature variability throughout the Holocene. Calcium content changes are related to regional bio-productivity changes in response to surface temperature changes with a pronounced deterioration at the beginning of the Neoglaciation and gradual enhancement during the late Holocene. Besides palaeoclimatic responses, the results offer the opportunity to study sediment transport and deposition during the regional deglaciation and mid-Holocene glacier growth in northwestern Fennoscandia. The temporal changes of the regional oceanography and the variability of marine palaeoproductivity in the South-Eastern Barents Sea indicate an active interplay between the North Atlantic Current (NAC) and the Norwegian Coastal Current (NCC) during the early Holocene, a predominance of the NCC during middle Holocene and a re-amplification of the NAC during the late Holocene. Comparison to other records from the Nordic Seas enables the reconstruction of responses and the vulnerability of this arctic marine ecosystem to past climate variations and may help to estimate upcoming responses to recent and future climate changes.</p><p> </p><p>References:</p><p>Snowball, I., L. Zillén, A. Ojala, T. Saarinen, and P. Sandgren (2007), FENNOSTACK and FENNORPIS: Varve dated Holocene palaeomagnetic secular variation and relative palaeointensity stacks for Fennoscandia, Earth and Planetary Science Letters, 255, (1-2), 106–116</p><p>Sagnotti, L., P. Macrì, R. Lucchi, M. Rebesco, and A. Camerlenghi (2011), A Holocene paleosecular variation record from the northwestern Barents Sea continental margin, Geochemistry, Geophysics, Geosystems, 12, (11)</p>

Exploring the Growing Role of Terrestrial Carbon Across North Atlantic Fjords

2020 ◽  
Author(s):  
Craig Smeaton ◽  
William Austin
Keyword(s):  
Organic Carbon ◽  
Marine Environment ◽  
North Atlantic ◽  
Planetary Science ◽  
Terrestrial Environment ◽  
Carbon Burial ◽  
Organic Carbon Burial ◽  
Fjord Sediments

<p>Fjords are recognized as globally significant hotspots for the burial (Smith et al., 2015) and long-term storage (Smeaton et al., 2017) of marine and terrestrially derived organic carbon (OC). By trapping and locking away OC over geological timescales, fjord sediments provide a potentially important yet largely overlooked climate regulation service. The proximity of fjords to the terrestrial environment in combination with their geomorphology and hydrography results in the fjordic sediments being subsidized with organic carbon (OC) from the terrestrial environment. This terrestrial OC (OC<sub>terr</sub>) transferred to the marine environment has traditionally be considered lost to the atmosphere in the form of CO<sub>2</sub> in most carbon (C) accounting schemes yet globally it is estimated that 55% of OC trapped in fjord sediments is derived from terrestrial sources (Cui et al., 2016). So is this terrestrial OC truly lost? Here, we estimate the quantity of OC<sub>terr</sub> held within North Atlantic fjords with the aim of better understanding the recent and long-term role of the terrestrial environment in the evolution of these globally significant sedimentary OC stores. By understanding this subsidy of OC from the terrestrial to the marine environment we can take the first steps in quantifying the terrestrial OC stored in fjords and the wider coastal marine environment.</p><p>Cui, X., Bianchi, T.S., Savage, C. and Smith, R.W., 2016. Organic carbon burial in fjords: Terrestrial versus marine inputs. <em>Earth and Planetary Science Letters</em>, <em>451</em>, pp.41-50.</p><p>Smeaton, C., Austin, W.E., Davies, A., Baltzer, A., Howe, J.A. and Baxter, J.M., 2017. Scotland's forgotten carbon: a national assessment of mid-latitude fjord sedimentary stocks. <em>Biogeosciences</em>.</p><p>Smith, R.W., Bianchi, T.S., Allison, M., Savage, C. and Galy, V., 2015. High rates of organic carbon burial in fjord sediments globally. <em>Nature Geoscience</em>, <em>8</em>(6), p.450.</p><p> </p>

Modulation of the Global Atmospheric Circulation by Combined Activity in the Madden–Julian Oscillation and the El Niño–Southern Oscillation during Boreal Winter

2010 ◽  
Vol 23 (15) ◽  
pp. 4045-4059 ◽  
Author(s):  
Paul E. Roundy ◽  
Kyle MacRitchie ◽  
Jonas Asuma ◽  
Timothy Melino
Keyword(s):  
North Atlantic ◽  
El Niño ◽  
El Nino ◽  
Southern Oscillation ◽  
El Niño Southern Oscillation ◽  
El Nino Southern Oscillation ◽  
Boreal Winter ◽  
Madden Julian Oscillation ◽  
The North ◽  
The North Atlantic

Abstract Composite global patterns associated with the El Niño–Southern Oscillation (ENSO) and the Madden–Julian oscillation (MJO) are frequently applied to help make predictions of weather around the globe at lead times beyond a few days. However, ENSO modulates the background states through which the MJO and its global response patterns propagate. This paper explores the possibility that nonlinear variations confound the combined use of composites based on the MJO and ENSO separately. Results indicate that when both modes are active at the same time, the associated patterns in the global flow are poorly represented by simple linear combinations of composites based on the MJO and ENSO individually. Composites calculated by averaging data over periods when both modes are present at the same time more effectively describe the associated weather patterns. Results reveal that the high-latitude response to the MJO varies with ENSO over all longitudes, but especially across the North Pacific Rim, North America, and the North Atlantic. Further analysis demonstrates that the MJO influence on indexes of the North Atlantic Oscillation is greatest during La Niña conditions or during periods of rapid adjustment in the phase of ENSO.

scholarly journals Precursory atmospheric circulations with Rossby wave trains leading to Eurasian extreme cold events

2021 ◽  
Author(s):  
Wenqin zhuo ◽  
Fei Huang ◽  
Ruichang Ding ◽  
Jin Luo
Keyword(s):  
Rossby Wave ◽  
North Atlantic ◽  
Wave Train ◽  
Teleconnection Pattern ◽  
Boreal Winter ◽  
Formation Mechanisms ◽  
Baffin Bay ◽  
Atmospheric Circulations ◽  
Westerly Jet ◽  
Wave Trains

Abstract This work examines precursory atmospheric circulations with various wave trains contributing to extreme cooling over central Eurasia in boreal winter from 1979-2016 based on the ERA-Interim dataset. The empirical orthogonal function (EOF) method is used to classify the anomalous sea level pressure field averaged in two weeks prior to extreme cooling. Based on the classification, three types of precursory atmospheric circulation patterns are named according to the origins of wave trains, and their formation mechanisms are revealed as well . Type1: Baffin Bay-origin pattern, which forms in the downstream development of Rossby wave packets generated from the downward stratospheric energy transmission over the Baffin Bay. Type2: Pacific-origin pattern, similar to a Eurasian (EU) teleconnection pattern, arises at the exit area of the westerly jet in the central North Pacific where cyclonic shear exists; then it develops along the northerly westerly jet over the North Atlantic, which may act as a waveguide to the Eurasian continent. Type 3: Atlantic-origin, manifests as the negative phase of type 2, consistent with the Scandinavian (SCAND) pattern, which may results from the air-sea interaction induced by the warm anomaly of sea surface temperature in the middle of North Atlantic. In conclusion, the three types of precursory atmospheric wave train patterns that bring extreme cooling to Eurasia possess diverse disturbing sources and development mechanisms. The results, which are investigated based on a quasi-biweekly time scale , deepen our understanding of the atmospheric genesis of extreme weather and have specific indicative significance to improve the technique of extended forecast.

scholarly journals Lessons from a high CO2 world: an ocean view from ~3 million years ago

2020 ◽  
Author(s):  
Erin McClymont ◽  
Heather Ford ◽  
Sze Ling Ho ◽  
Julia Tindall ◽  
Alan Haywood ◽  
...  
Keyword(s):  
Ocean Circulation ◽  
North Atlantic ◽  
Spatial Scales ◽  
Climate System ◽  
Sea Surface ◽  
System Response ◽  
Emission Scenarios ◽  
Proxy Data ◽  
Mean Sea Surface ◽  
Global Mean

<p>A range of future climate scenarios are projected for high atmospheric CO<sub>2</sub> concentrations, given uncertainties over future human actions as well as potential environmental and climatic feedbacks. The geological record offers an opportunity to understand climate system response to a range of forcings and feedbacks which operate over multiple temporal and spatial scales. Here, we examine a single interglacial during the late Pliocene (KM5c, ca. 3.205 +/- 0.01 Ma) when atmospheric CO<sub>2</sub> concentrations were higher than pre-industrial, but similar to today and to the lowest emission scenarios for this century. As orbital forcing and continental configurations were almost identical to today, we are able to focus on equilibrium climate system response to modern and near-future CO<sub>2</sub>. Using proxy data from 32 sites, we demonstrate that global mean sea-surface temperatures were warmer than pre-industrial, by ~2.3 ºC for the combined proxy data (foraminifera Mg/Ca and alkenones), or by ~3.2ºC (alkenones only). Compared to the pre-industrial, reduced meridional gradients and enhanced warming in the North Atlantic are consistently reconstructed. There is broad agreement between data and models at the global scale, with regional differences reflecting ocean circulation and/or proxy signals. An uneven distribution of proxy data in time and space does, however, add uncertainty to our anomaly calculations. The reconstructed global mean sea-surface temperature anomaly for KM5c is warmer than all but three of the PlioMIP2 model outputs, and the reconstructed North Atlantic data tend to align with the warmest KM5c model values.  Our results demonstrate that even under low CO<sub>2</sub> emission scenarios, surface ocean warming may be expected to exceed model projections, and will be accentuated in the higher latitudes.</p>

scholarly journals Longitude-dependent decadal ozone changes and ozone trends in boreal winter months during 1960–2000

2008 ◽  
Vol 26 (5) ◽  
pp. 1275-1286 ◽  
Author(s):  
D. H. W. Peters ◽  
A. Gabriel ◽  
G. Entzian
Keyword(s):  
Rossby Wave ◽  
North Atlantic ◽  
Total Ozone ◽  
Planetary Wave ◽  
Wave Structure ◽  
Boreal Winter ◽  
The North ◽  
The North Atlantic ◽  
Eastern North Atlantic ◽  
The 1960S

Abstract. This study examines the longitude-dependent decadal changes and trends of ozone for the boreal winter months during the period of 1960–2000. These changes are caused primarily by changes in the planetary wave structure in the upper troposphere and lower stratosphere. The decadal changes and trends over 4 decades of geopotential perturbations, defined as a deviation from the zonal mean, are estimated by linear regression with time. The decadal changes in longitude-dependent ozone were calculated with a simple transport model of ozone based on the known planetary wave structure changes and prescribed zonal mean ozone gradients. For December of the 1960s and 1980s a statistically significant Rossby wave track appeared over the North Atlantic and Europe with an anticyclonic disturbance over the Eastern North Atlantic and Western Europe, flanked by cyclonic disturbances. In the 1970s and 1990s statistically significant cyclonic disturbances appeared over the Eastern North Atlantic and Europe, surrounded by anticyclonic anomalies over Northern Africa, Central Asia and Greenland. Similar patterns have been found for January. The Rossby wave track over the North Atlantic and Europe is stronger in the 1980s than in the 1960s. For February, the variability of the regression patterns is higher. For January we found a strong alteration in the modelled decadal changes in total ozone over Central and Northern Europe, showing a decrease of about 15 DU in the 1960s and 1980s and an increase of about 10 DU in the 1970s and 1990s. Over Central Europe the positive geopotential height trend (increase of 2.3 m/yr) over 40 years is of the same order (about 100 m) as the increase in the 1980s alone. This is important to recognize because it implies a total ozone decrease over Europe of the order of 14 DU for the 1960–2000 period, for January, if we use the standard change regression relation that about a 10-m geopotential height increase at 300 hPa is related to about a 1.4-DU total ozone decrease.

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