scholarly journals Winter–spring warming in the North Atlantic during the last 2000 years: evidence from southwest Iceland

2021 ◽  
Vol 17 (3) ◽  
pp. 1363-1383
Author(s):  
Nora Richter ◽  
James M. Russell ◽  
Johanna Garfinkel ◽  
Yongsong Huang
Keyword(s):  
Ocean Circulation ◽  
Climate Model ◽  
Sea Surface ◽  
Balance Model ◽  
Sea Surface Temperatures ◽  
Spring Season ◽  
Spring Warming ◽  
Surface Temperatures ◽  
Air Temperatures ◽  
Spring Temperatures

Abstract. Temperature reconstructions from the Northern Hemisphere (NH) generally indicate cooling over the Holocene, which is often attributed to decreasing summer insolation. However, climate model simulations predict that rising atmospheric CO2 concentrations and the collapse of the Laurentide Ice Sheet caused mean annual warming during this epoch. This contrast could reflect a seasonal bias in temperature proxies, and particularly a lack of proxies that record cold (late fall–early spring) season temperatures, or inaccuracies in climate model predictions of NH temperature. We reconstructed winter–spring temperatures during the Common Era (i.e., the last 2000 years) using alkenones, lipids produced by Isochrysidales haptophyte algae that bloom during spring ice-out, preserved in sediments from Vestra Gíslholtsvatn (VGHV), southwest Iceland. Our record indicates that winter–spring temperatures warmed during the last 2000 years, in contrast to most NH averages. Sensitivity tests with a lake energy balance model suggest that warmer winter and spring air temperatures result in earlier ice-out dates and warmer spring lake water temperatures and therefore warming in our proxy record. Regional air temperatures are strongly influenced by sea surface temperatures during the winter and spring season. Sea surface temperatures (SSTs) respond to both changes in ocean circulation and gradual changes in insolation. We also found distinct seasonal differences in centennial-scale, cold-season temperature variations in VGHV compared to existing records of summer and annual temperatures from Iceland. Multi-decadal to centennial-scale changes in winter–spring temperatures were strongly modulated by internal climate variability and changes in regional ocean circulation, which can result in winter and spring warming in Iceland even after a major negative radiative perturbation.

Quantifying Teleconnection pathways leading to Low Rainfall anomalies during Boreal Summer in Indonesian Borneo

2021 ◽  
Author(s):  
Timothy Lam ◽  
Marlene Kretschmer ◽  
Samantha Adams ◽  
Alberto Arribas ◽  
Rachel Prudden ◽  
...  
Keyword(s):  
Causal Inference ◽  
Climate Model ◽  
Southern Oscillation ◽  
Sea Surface ◽  
Boreal Summer ◽  
Climate Indices ◽  
Sea Surface Temperatures ◽  
Study Region ◽  
Surface Temperatures ◽  
Rainfall Anomalies

<p>Teleconnections are sources of predictability for regional weather and climate, which can be represented by causal relationships between climate features in physically separated regions. In this study, teleconnections of low rainfall anomalies in Indonesian Borneo are analysed and quantified using causal inference theory and causal networks. Causal hypotheses are first developed based on climate model experiments in literature and then justified by means of partial regression analysis between NCEP reanalysis sea surface temperatures and climate indices (drivers) and rainfall data in Indonesian Borneo from various sources (target variable). We find that, as previous studies have highlighted, El Niño Southern Oscillation (ENSO) has a profound effect on rainfall in Indonesia Borneo, with positive Niño 3.4 index serving as a direct driver of low rainfall, also partially through reduced sea surface temperatures (SSTs) over Indonesian waters. On the other hand, while Indian Ocean Dipole (IOD) influences Indonesian Borneo rainfall through SSTs over the same area as a thermodynamic effect, its remaining effect has shifted at multidecadal timescale, opening the rooms for further research. This work informs the potential of a systematic causal approach to statistical inference as a powerful tool to verify and explore atmospheric teleconnections and enables seasonal forecasting to strengthen prevention and control of drought and fire multihazards over peatlands in the study region.</p><p>Keywords: Tropical teleconnections, Causal inference, Climate variability, Drought, Indonesia</p>

tamh tm iedor sphere -1 el 9a8 ti 0vse , lyc li s m im a p te le models. Much more detailed than in the Australian region (Simpson and Downey 1975; run. Rather they are models than simp allysofomuuscehdm ro ourte in eelxypesn in si cvee th to e V ha osicbe ee anndfoH rc uendt 198 recasting El Nino behav­ tures for the p w er iitohd4o ). bsT1eh rv e BMRC climate model iour (e.g., sea surface temperatures in the east simulated by the model ha 9s49e -d 9 1 se , aasnud rf ac th eet em ra p in efraal ­ lfeoqrueactaosrti al r Pacific), they could, in theory, be used to ob been compared with the coupling o ai fnftahleloacnedantetmoptehrea tu artemoosvpehre re la nidn . th Tehseew te asse rv ru end ra fiinvfea ll t i ( m Fr eesd , er w ik istehne th teal. s1a9m9e5 ). seTahesm ur o fa dceelmmo od deellss , ( hPoowweevrere , tis less than perfect. Improved ocean ph m er p ic e ra ctoun re d s it io bnust . s T li h ghtly different starting atmos­ these coupled mode alls . . 1995) are being developed for ialg lu rseterm ate esnttw he it h ‘ noobisseer ’ veind iffe ed rtahier ence betw nfa m ll, o w de e l . neTeoenge th t e ed to av mru uns O era cghep se aarsto ne pro onfalthperebd le ic m ti own it ihstthheeduisfef ic oufltcy oupled models in all five runs as an ‘ens coupled models has in sitmhue la attim ng osrp ai hnefrailclA of u st p ra rleicainpp it raetc io ip n i tat sihoon, w em abtls le’. eoam st e The en o ve srkin ll sem o rt ihne bl sei ave rn Amuusl rag t a ra ti lnegsgoennte he ia. (Ni ra l sp su a c ti caelsssca in le ssiimmuploartt in an gtaftomrousspeh rs e , ridcesvpairtieab th il e it iyr Fur T th h e es resoau tm th o , stphheem ri odels are less successful. sea cshuo rf l a ls ce1t9e9m6p ) e . ra M tu ordeealneoxmpaelriiemsehnatvsewailtohngspheicsitfo ie ry djtohb er e o fo f re si m pr uolbaa ti bnlgyc th cemSoOdIel ( eFx ig pe urrieme3n .3 ts ) . do ThaegSoO od I an be predicted without the need

Droughts ◽  
2016 ◽  
pp. 77-77
Keyword(s):  
El Niño ◽  
Climate Model ◽  
El Nino ◽  
Sea Surface ◽  
Sea Surface Temperatures ◽  
Coupled Models ◽  
Coupled Mode ◽  
Australian Region ◽  
Surface Temperatures

The Transient Circulation Response to Radiative Forcings and Sea Surface Warming*

2014 ◽  
Vol 27 (24) ◽  
pp. 9323-9336 ◽  
Author(s):  
Paul W. Staten ◽  
Thomas Reichler ◽  
Jian Lu
Keyword(s):  
General Circulation ◽  
Climate Model ◽  
Stratospheric Ozone ◽  
Sea Surface ◽  
Sea Surface Temperatures ◽  
Indirect Response ◽  
Radiative Forcings ◽  
Surface Warming ◽  
Impact Surface ◽  
Surface Temperatures

Abstract Tropospheric circulation shifts have strong potential to impact surface climate. However, the magnitude of these shifts in a changing climate and the attending regional hydrological changes are difficult to project. Part of this difficulty arises from the lack of understanding of the physical mechanisms behind the circulation shifts themselves. To better delineate circulation shifts and their respective causes the circulation response is decomposed into 1) the “direct” response to radiative forcings themselves and 2) the “indirect” response to changing sea surface temperatures. Using ensembles of 90-day climate model simulations with immediate switch-on forcings, including perturbed greenhouse gas concentrations, stratospheric ozone concentrations, and sea surface temperatures, this paper documents the direct and indirect transient responses of the zonal-mean general circulation, and investigates the roles of previously proposed mechanisms in shifting the midlatitude jet. It is found that both the direct and indirect wind responses often begin in the lower stratosphere. Changes in midlatitude eddies are ubiquitous and synchronous with the midlatitude zonal wind response. Shifts in the critical latitude of wave absorption on either flank of the jet are not indicted as primary factors for the poleward-shifting jet, although some evidence for increasing equatorward wave reflection over the Southern Hemisphere in response to sea surface warming is seen. Mechanisms for the Northern Hemisphere jet shift are less clear.

Evolution of Water Vapor Concentrations and Stratospheric Age of Air in Coupled Chemistry-Climate Model Simulations

2007 ◽  
Vol 64 (3) ◽  
pp. 905-921 ◽  
Author(s):  
John Austin ◽  
John Wilson ◽  
Feng Li ◽  
Holger Vömel
Keyword(s):  
Water Vapor ◽  
Greenhouse Gas ◽  
Climate Model ◽  
Sea Surface ◽  
Time Slice ◽  
Sea Surface Temperatures ◽  
Model Simulations ◽  
Stratospheric Water Vapor ◽  
Surface Temperatures ◽  
Climate Model Simulations

Abstract Stratospheric water vapor concentrations and age of air are investigated in an ensemble of coupled chemistry-climate model simulations covering the period from 1960 to 2005. Observed greenhouse gas concentrations, halogen concentrations, aerosol amounts, and sea surface temperatures are all specified in the model as time-varying fields. The results are compared with two experiments (time-slice runs) with constant forcings for the years 1960 and 2000, in which the sea surface temperatures are set to the same climatological values, aerosol concentrations are fixed at background levels, while greenhouse gas and halogen concentrations are set to the values for the relevant years. The time-slice runs indicate an increase in stratospheric water vapor from 1960 to 2000 due primarily to methane oxidation. The age of air is found to be significantly less in the year 2000 run than the 1960 run. The transient runs from 1960 to 2005 indicate broadly similar results: an increase in water vapor and a decrease in age of air. However, the results do not change gradually. The age of air decreases significantly only after about 1975, corresponding to the period of ozone reduction. The age of air is related to tropical upwelling, which determines the transport of methane into the stratosphere. Oxidation of increased methane from enhanced tropical upwelling results in higher water vapor amounts. In the model simulations, the rate of increase of stratospheric water vapor during the period of enhanced upwelling is up to twice the long-term mean. The concentration of stratospheric water vapor also increases following volcanic eruptions during the simulations.

scholarly journals Linking catchment hydrology and ocean circulation in Late Holocene southernmost Africa

2016 ◽  
Author(s):  
Annette Hahn ◽  
Enno Schefuß ◽  
Sergio Andó ◽  
Hayley C. Cawthraw ◽  
Peter Frenzel ◽  
...  
Keyword(s):  
South Africa ◽  
Ocean Circulation ◽  
Climatic Conditions ◽  
Sea Surface ◽  
Ice Age ◽  
Time Interval ◽  
Sea Surface Temperatures ◽  
Surface Temperatures ◽  
Precipitation Regimes ◽  
Climatic System

Abstract. Recent studies of the South African climatic system revealed a highly complex interplay of forcing factors on precipitation regimes. This includes the influence of the tropical easterlies, the strength of the Southern Hemispheric Westerlies as well as sea surface temperatures along the coast of the subcontinent. This study of a sediment core at the terrestrial-marine interface spanning a time interval of ~ 4 ka provides insights on the highly dynamic climatic system in southernmost South Africa. Several organic proxies sensitive to changes in climatic parameters like the distribution and isotopic composition of plant-wax lipids as well as indicators for sea surface temperatures and soil input give information on climatic changes during the investigated time period. Moreover, the micropaleontology, mineralogical and elemental composition of the sediments reflects the variability of the terrigenous input to the core site. The combination of downcore sediment signatures and a catchment-wide provenance study indicate that the Little Ice Age was characterized by relatively warm sea surface temperatures in Mossel Bay and arid climatic conditions favorable to torrential flood events sourced in the Gouritz headlands. In contrast, the so-called Medieval Climate Anomaly is expressed by humid conditions in the Gouritz River catchment with lower, but highly variable sea surface temperatures in the Mossel Bay area. The coincidence between humid climatic conditions and cooler sea surface temperatures has been attributed to a strengthened and more southerly anticyclonic circulation. In this climatic setting strong tropical easterlies supply Indian Ocean moisture to South Africa and at the same time Agulhas Bank upwelling pulses become more common due to an increase in Agulhas Current transport as well as alongshore southeasterly winds. These processes resemble the modern day oceanography in summer and can be conceptualized in a regional climate model.

scholarly journals Glacial to Holocene changes in trans-Atlantic Saharan dust transport and dust-climate feedbacks

2016 ◽  
Vol 2 (11) ◽  
pp. e1600445 ◽  
Author(s):  
Ross H. Williams ◽  
David McGee ◽  
Christopher W. Kinsley ◽  
David A. Ridley ◽  
Shineng Hu ◽  
...  
Keyword(s):  
North Atlantic ◽  
Radiative Forcing ◽  
Climate Model ◽  
Regional Climate ◽  
Sea Surface ◽  
Saharan Dust ◽  
Sea Surface Temperatures ◽  
Dust Transport ◽  
Surface Temperatures ◽  
Tropical North Atlantic

Saharan mineral dust exported over the tropical North Atlantic is thought to have significant impacts on regional climate and ecosystems, but limited data exist documenting past changes in long-range dust transport. This data gap limits investigations of the role of Saharan dust in past climate change, in particular during the mid-Holocene, when climate models consistently underestimate the intensification of the West African monsoon documented by paleorecords. We present reconstructions of African dust deposition in sediments from the Bahamas and the tropical North Atlantic spanning the last 23,000 years. Both sites show early and mid-Holocene dust fluxes 40 to 50% lower than recent values and maximum dust fluxes during the deglaciation, demonstrating agreement with records from the northwest African margin. These quantitative estimates of trans-Atlantic dust transport offer important constraints on past changes in dust-related radiative and biogeochemical impacts. Using idealized climate model experiments to investigate the response to reductions in Saharan dust’s radiative forcing over the tropical North Atlantic, we find that small (0.15°C) dust-related increases in regional sea surface temperatures are sufficient to cause significant northward shifts in the Atlantic Intertropical Convergence Zone, increased precipitation in the western Sahel and Sahara, and reductions in easterly and northeasterly winds over dust source regions. Our results suggest that the amplifying feedback of dust on sea surface temperatures and regional climate may be significant and that accurate simulation of dust’s radiative effects is likely essential to improving model representations of past and future precipitation variations in North Africa.

Revised Southern Ocean sea surface temperatures over the last 180 ka

2021 ◽  
Author(s):  
David Chandler ◽  
Petra Langebroek
Keyword(s):  
Southern Ocean ◽  
Sea Level ◽  
Climate Model ◽  
Ice Sheet ◽  
Sea Surface ◽  
Sea Surface Temperatures ◽  
Last Interglacial ◽  
Antarctic Ice Sheet ◽  
Surface Temperatures ◽  
Temperature Reconstructions

<p>Proxy records and climate models suggest that the Last Interglacial (LIG, ~130 to 115 thousand years before present) was characterised by high-latitude air and sea surface temperatures (SSTs) slightly warmer than present, and by mean global sea level a few metres higher. Therefore, the LIG is widely used as an analogue for near-future oceanographic/climatic conditions. Of particular interest is the Antarctic Ice Sheet’s contribution to rapid sea level rise and to Southern Ocean surface freshening, in response to warming. In the Southern Ocean, existing LIG temperature reconstructions suffer from very high variance amongst a low number of individual records. Recent syntheses have focused on the LIG climatic optimum, but conditions during the penultimate glacial are also important for forcing transient climate or Antarctic Ice Sheet simulations. Here we use databases of modern core-top sediments to evaluate the strengths of SST proxies available in the Southern Ocean, and consider their likely sources of bias and variance. By selecting only those paleo-temperature reconstructions which we believe are reliable in this region, we then compile a Southern Ocean SST synthesis covering the penultimate glacial and the LIG. This longer temperature time series can be used as a basis for LIG ice sheet simulations or for climate model development.  </p>

Impacts of Shortwave Penetration Depth on Large-Scale Ocean Circulation and Heat Transport

2005 ◽  
Vol 35 (6) ◽  
pp. 1103-1119 ◽  
Author(s):  
Colm Sweeney ◽  
Anand Gnanadesikan ◽  
Stephen M. Griffies ◽  
Matthew J. Harrison ◽  
Anthony J. Rosati ◽  
...  
Keyword(s):  
Heat Flux ◽  
Heat Transport ◽  
Penetration Depth ◽  
Ocean Circulation ◽  
Mixed Layer ◽  
Large Scale ◽  
Sea Surface ◽  
Shortwave Radiation ◽  
Sea Surface Temperatures ◽  
Surface Temperatures

Abstract The impact of changes in shortwave radiation penetration depth on the global ocean circulation and heat transport is studied using the GFDL Modular Ocean Model (MOM4) with two independent parameterizations that use ocean color to estimate the penetration depth of shortwave radiation. Ten to eighteen percent increases in the depth of 1% downwelling surface irradiance levels results in an increase in mixed layer depths of 3–20 m in the subtropical and tropical regions with no change at higher latitudes. While 1D models have predicted that sea surface temperatures at the equator would decrease with deeper penetration of solar irradiance, this study shows a warming, resulting in a 10% decrease in the required restoring heat flux needed to maintain climatological sea surface temperatures in the eastern equatorial Atlantic and Pacific Oceans. The decrease in the restoring heat flux is attributed to a slowdown in heat transport (5%) from the Tropics and an increase in the temperature of submixed layer waters being transported into the equatorial regions. Calculations were made using a simple relationship between mixed layer depth and meridional mass transport. When compared with model diagnostics, these calculations suggest that the slowdown in heat transport is primarily due to off-equatorial increases in mixed layer depths. At higher latitudes (5°–40°), higher restoring heat fluxes are needed to maintain sea surface temperatures because of deeper mixed layers and an increase in storage of heat below the mixed layer. This study offers a way to evaluate the changes in irradiance penetration depths in coupled ocean–atmosphere GCMs and the potential effect that large-scale changes in chlorophyll a concentrations will have on ocean circulation.

scholarly journals Late Paleocene–early Eocene Arctic Ocean sea surface temperatures: reassessing biomarker paleothermometry at Lomonosov Ridge

2020 ◽  
Vol 16 (6) ◽  
pp. 2381-2400 ◽  
Author(s):  
Appy Sluijs ◽  
Joost Frieling ◽  
Gordon N. Inglis ◽  
Klaas G. J. Nierop ◽  
Francien Peterse ◽  
...  
Keyword(s):  
Climate Models ◽  
Sea Surface ◽  
Temperature Sensitive ◽  
Lomonosov Ridge ◽  
Early Eocene ◽  
Sea Surface Temperatures ◽  
Surface Temperatures ◽  
Late Paleocene ◽  
Air Temperatures ◽  
Thermal Maximum

Abstract. A series of papers published shortly after the Integrated Ocean Drilling Program Arctic Coring Expedition (ACEX, 2004) on Lomonosov Ridge indicated remarkably high early Eocene sea surface temperatures (SSTs; ca. 23 to 27 ∘C) and land air temperatures (ca. 17 to 25 ∘C) based on the distribution of isoprenoid and branched glycerol dialkyl glycerol tetraether (isoGDGT and brGDGT) lipids, respectively. Here, we revisit these results using recent analytical developments – which have led to improved temperature calibrations and the discovery of new temperature-sensitive glycerol monoalkyl glycerol tetraethers (GMGTs) – and currently available proxy constraints. The isoGDGT assemblages support temperature as the dominant variable controlling TEX86 values for most samples. However, contributions of isoGDGTs from land, which we characterize in detail, complicate TEX86 paleothermometry in the late Paleocene and part of the interval between the Paleocene–Eocene Thermal Maximum (PETM; ∼ 56 Ma) and the Eocene Thermal Maximum 2 (ETM2; ∼ 54 Ma). Background early Eocene SSTs generally exceeded 20 ∘C, with peak warmth during the PETM (∼ 26 ∘C) and ETM2 (∼ 27 ∘C). We find abundant branched GMGTs, likely dominantly marine in origin, and their distribution responds to environmental change. Further modern work is required to test to what extent temperature and other environmental factors determine their distribution. Published Arctic vegetation reconstructions indicate coldest-month mean continental air temperatures of 6–13 ∘C, which reinforces the question of whether TEX86-derived SSTs in the Paleogene Arctic are skewed towards the summer season. The exact meaning of TEX86 in the Paleogene Arctic thus remains a fundamental issue, and it is one that limits our assessment of the performance of fully coupled climate models under greenhouse conditions.

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