scholarly journals Effect of changing ocean circulation on deep ocean temperature in the last millennium

2020 ◽  
Author(s):  
Jeemijn Scheen ◽  
Thomas F. Stocker
Keyword(s):  
Surface Temperature ◽  
Ocean Circulation ◽  
Little Ice Age ◽  
Heat Content ◽  
Deep Ocean ◽  
Ice Age ◽  
Ocean Temperature ◽  
Meridional Heat Transport ◽  
Temperature Anomalies ◽  
The Past

Abstract. Paleoreconstructions and modern observations provide us with anomalies of surface temperature over the past millennium. The history of deep ocean temperatures is much less well-known and was simulated in a recent study for the past 2000 years under forced surface temperature anomalies. In this study, we simulate the past 800 years with an illustrative forcing scenario in the Bern3D ocean model, which enables us to assess the role of changes in ocean circulation on deep ocean temperature. We quantify the effect of changing ocean circulation by comparing transient simulations (where the ocean dynamically adjusts to anomalies in surface temperature – hence density) to simulations with fixed ocean circulation. We decompose temperature, ocean heat content and meridional heat transport into the contributions from changing ocean circulation and changing sea surface temperature (SST). In the deep ocean, the contribution from changing ocean circulation is found to be as important as the changing SST signal itself. Firstly, the small changes in ocean circulation amplify the Little Ice Age signal around 3 km depth by at least a factor of two, depending on the basin. Secondly, they fasten the arrival of this atmospheric signal in the Pacific and Southern Ocean at all depths, whereas they delay the arrival in the Atlantic between about 2.5 and 3.5 km by two centuries. This delay is explained by an initial competition between the Little Ice Age cooling and a warming due to an increase in relatively warmer North Atlantic Deep Water at the cost of Antarctic Bottom Water. Under the consecutive AMOC slowdown, this shift in water masses is inverted and aging of the water causes a late additional cooling. Our results suggest that small changes in ocean circulation can have a large impact on the amplitude and timing of ocean temperature anomalies below 2 km depth.

scholarly journals Effect of changing ocean circulation on deep ocean temperature in the last millennium

2020 ◽  
Vol 11 (4) ◽  
pp. 925-951
Author(s):  
Jeemijn Scheen ◽  
Thomas F. Stocker
Keyword(s):  
Surface Temperature ◽  
Ocean Circulation ◽  
Little Ice Age ◽  
Deep Ocean ◽  
Meridional Overturning Circulation ◽  
Ice Age ◽  
Ocean Temperature ◽  
Temperature Anomalies ◽  
The Past ◽  
The Impact

Abstract. Paleoreconstructions and modern observations provide us with anomalies of surface temperature over the past millennium. The history of deep ocean temperatures is much less well-known and was simulated in a recent study for the past 2000 years under forced surface temperature anomalies and fixed ocean circulation. In this study, we simulate the past 800 years with an illustrative forcing scenario in the Bern3D ocean model, which enables us to assess the impact of changes in ocean circulation on deep ocean temperature. We quantify the effect of changing ocean circulation by comparing transient simulations (where the ocean dynamically adjusts to anomalies in surface temperature – hence density) to simulations with fixed ocean circulation. We decompose temperature, ocean heat content and meridional heat transport into the contributions from changing ocean circulation and changing sea surface temperature (SST). In the deep ocean, the contribution from changing ocean circulation is found to be as important as the changing SST signal itself. Firstly, the small changes in ocean circulation amplify the Little Ice Age signal at around 3 km depth by at least a factor of 2, depending on the basin. Secondly, they fasten the arrival of this atmospheric signal in the Pacific and Southern Ocean at all depths, whereas they delay the arrival in the Atlantic between about 2.5 and 3.5 km by two centuries. This delay is explained by an initial competition between the Little Ice Age cooling and a warming due to an increase in relatively warmer North Atlantic Deep Water at the cost of Antarctic Bottom Water. Under the consecutive Atlantic meridional overturning circulation (AMOC) slowdown, this shift in water masses is inverted and ageing of the water causes a late additional cooling. Our results suggest that small changes in ocean circulation can have a large impact on the amplitude and timing of ocean temperature anomalies below 2 km depth.

Climatic Variation and Changes in the Wind and Ocean Circulation: The Little Ice Age in the Northeast Atlantic

1979 ◽  
Vol 11 (1) ◽  
pp. 1-20 ◽  
Author(s):  
Hubert H. Lamb
Keyword(s):  
Surface Temperature ◽  
Sea Surface Temperature ◽  
Ocean Circulation ◽  
Little Ice Age ◽  
Sea Surface ◽  
Ice Age ◽  
The Arctic ◽  
The North ◽  
The North Sea ◽  
Polar Water

Variations must take place in the ocean circulation when the general wind circulation varies. There are hints even within recent years that the variations in the ocean between Iceland and Scotland and Norway can be big: The area has been regarded as the main path of the warm, saline North Atlantic Drift water heading towards the Arctic; but, when the polar water occasionally intrudes from the north, sea-surface temperature is liable to fall by 3 to 5°C and presumably by more than this when, as in 1888, the ice advanced to near the Faeroe Islands. The long series of sea-surface temperature observations at that point, starting in 1867, and earlier observations covering the area in 1789, are studied. Various kinds of proxy data—notably the CLIMAP Atlantic ocean-bed core analysis results for the last Ice Age climax and cod fishery and sea-ice reports from the Little Ice Age in the 17th century AD —are then used to indicate the variability in this part of the ocean on longer time scales. The reconstruction of the situation between ad 1675 and 1705 resulting from this study suggests a probable mean departure of the sea surface temperature from modern values between the Faeroes and southeast Iceland amounting to about −5°C; and at the climax in 1695 the polar water seems to have spread all around Iceland, across the entire surface of the Norwegian Sea to Norway, and south to near Shetland. Support for this diagnosis is found in a considerable variety of reports of environmental conditions existing at the time in Scotland, south Norway and elsewhere. The enhanced thermal gradient between approximately latitudes 55 and 65°N during the Little Ice Age, which this result indicates, offers an explanation for the occurrence in that period of a number of windstorms which changed the coasts in various places and seem to have surpassed in intensity the worst experienced in the region in more recent times.

The Little Ice Age and 20th-century deep Pacific cooling

Science ◽  
2019 ◽  
Vol 363 (6422) ◽  
pp. 70-74 ◽  
Author(s):  
G. Gebbie ◽  
P. Huybers
Keyword(s):  
Long Memory ◽  
Little Ice Age ◽  
Deep Ocean ◽  
Ocean Model ◽  
Ice Age ◽  
Ocean Temperature ◽  
Temperature Changes ◽  
Surface Ocean ◽  
Proxy Records ◽  
Temperature Trends

Proxy records show that before the onset of modern anthropogenic warming, globally coherent cooling occurred from the Medieval Warm Period to the Little Ice Age. The long memory of the ocean suggests that these historical surface anomalies are associated with ongoing deep-ocean temperature adjustments. Combining an ocean model with modern and paleoceanographic data leads to a prediction that the deep Pacific is still adjusting to the cooling going into the Little Ice Age, whereas temperature trends in the surface ocean and deep Atlantic reflect modern warming. This prediction is corroborated by temperature changes identified between the HMS Challenger expedition of the 1870s and modern hydrography. The implied heat loss in the deep ocean since 1750 CE offsets one-fourth of the global heat gain in the upper ocean.

scholarly journals Nutrient utilisation and weathering inputs in the Peruvian upwelling region since the Little Ice Age

2015 ◽  
Vol 11 (2) ◽  
pp. 187-202 ◽  
Author(s):  
C. Ehlert ◽  
P. Grasse ◽  
D. Gutiérrez ◽  
R. Salvatteci ◽  
M. Frank
Keyword(s):  
Ocean Circulation ◽  
Little Ice Age ◽  
Isotope Composition ◽  
Nitrogen Loss ◽  
Nutrient Supply ◽  
Transitional Period ◽  
Ice Age ◽  
The Past ◽  
Nutrient Utilisation ◽  
Sediment Fraction

Abstract. For this study two sediment cores from the Peruvian shelf covering the time period between the Little Ice Age (LIA) and present were examined for changes in productivity (biogenic opal concentrations (bSi)), nutrient utilisation (stable isotope compositions of silicon (δ30Siopal) and nitrogen (δ15Nsed)), as well as in ocean circulation and material transport (authigenic and detrital radiogenic neodymium (ϵNd) and strontium (87Sr/86Sr) isotopes). For the LIA the proxies recorded weak primary productivity and nutrient utilisation reflected by low average bSi concentrations of ~10%, δ15Nsed values of ~5‰ and intermediate δ30Siopal values of ~0.9‰. At the same time, the radiogenic isotope composition of the detrital sediment fraction indicates dominant local riverine input of lithogenic material due to higher rainfall in the Andean hinterland. These patterns were most likely caused by permanent El Niño-like conditions characterised by a deeper nutricline, weak upwelling and low nutrient supply. At the end of the LIA, δ 30Siopal dropped to low values of +0.6‰ and opal productivity reached its minimum of the past 650 years. During the following transitional period of time the intensity of upwelling, nutrient supply and productivity increased abruptly as marked by the highest bSi contents of up to 38%, by δ15Nsed of up to ~7‰, and by the highest degree of silicate utilisation with δ30Siopal reaching values of +1.1‰. At the same time, detrital ϵNd and 87Sr/86Sr signatures documented increased wind strength and supply of dust to the shelf due to drier conditions. Since about 1870, productivity has been high but nutrient utilisation has remained at levels similar to the LIA, indicating significantly increased nutrient availability. Comparison between the δ30Siopal and δ15Nsed signatures suggests that during the past 650 years the δ15Nsed signature in the Peruvian upwelling area has to a large extent been controlled by surface water utilisation and not, as previously assumed, by subsurface nitrogen loss processes in the water column, which only had a significant influence during modern times (i.e. since ~AD 1870).

scholarly journals Nutrient utilisation and weathering inputs in the Peruvian upwelling region since the Little Ice Age

2014 ◽  
Vol 10 (4) ◽  
pp. 3357-3396 ◽  
Author(s):  
C. Ehlert ◽  
P. Grasse ◽  
D. Gutiérrez ◽  
R. Salvatteci ◽  
M. Frank
Keyword(s):  
Ocean Circulation ◽  
Little Ice Age ◽  
Isotope Composition ◽  
Nitrogen Loss ◽  
Nutrient Supply ◽  
Transitional Period ◽  
Ice Age ◽  
The Past ◽  
Nutrient Utilisation ◽  
Sediment Fraction

Abstract. For this study two sediment cores from the Peruvian shelf covering the time period between the Little Ice Age (LIA) and present were examined for changes in productivity (biogenic opal concentrations (bSi)), nutrient utilisation (stable isotope compositions of silicon (δ30Siopal) and nitrogen (δ15Nsed)), as well as in ocean circulation and material transport (authigenic and detrital radiogenic neodymium (εNd) and strontium (87Sr/86Sr) isotopes). For the LIA the proxies recorded weak primary productivity and nutrient utilisation reflected by low average bSi concentrations of ~10%, δ15Nsed values of ~ +5‰ and intermediate δ30Siopal values of ~+0.97‰. At the same time the radiogenic isotope composition of the detrital sediment fraction indicates dominant local riverine input of lithogenic material due to higher rainfall in the Andean hinterland. These patterns were caused by permanent El Niño-like conditions characterized by a deeper nutricline, weak upwelling and low nutrient supply. At the end of the LIA, δ30Siopal dropped to low values of +0.6‰ and opal productivity reached its minimum of the past 650 years. During the following transitional period of time the intensity of upwelling, nutrient supply and productivity increased abruptly as marked by the highest bSi contents of up to 38%, by δ15Nsed of up to ~ +7‰, and by the highest degree of silicate utilisation with δ30Siopal reaching values of +1.1‰. At the same time detrital εNd and 87Sr/86Sr signatures documented increased wind strength and supply of dust to the shelf due to drier conditions. Since about 1870, productivity has been high but nutrient utilisation has remained at levels similar to the LIA indicating significantly increased nutrient availability. Comparison between the δ30Siopal and δ15Nsed signatures suggests that during the past 650 years the δ15Nsed signature in the Peruvian Upwelling area has most likely primarily been controlled by surface water utilisation and not, as previously assumed, by subsurface nitrogen loss processes in the water column.

scholarly journals 20th century cooling of the deep ocean contributed to delayed acceleration of Earth’s energy imbalance

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
A. Bagnell ◽  
T. DeVries
Keyword(s):  
20Th Century ◽  
Heat Content ◽  
Deep Ocean ◽  
Ocean Warming ◽  
Ocean Heat Content ◽  
Global Ocean ◽  
Energy Imbalance ◽  
Delayed Onset ◽  
The Past ◽  
Historical Reconstructions

AbstractThe historical evolution of Earth’s energy imbalance can be quantified by changes in the global ocean heat content. However, historical reconstructions of ocean heat content often neglect a large volume of the deep ocean, due to sparse observations of ocean temperatures below 2000 m. Here, we provide a global reconstruction of historical changes in full-depth ocean heat content based on interpolated subsurface temperature data using an autoregressive artificial neural network, providing estimates of total ocean warming for the period 1946-2019. We find that cooling of the deep ocean and a small heat gain in the upper ocean led to no robust trend in global ocean heat content from 1960-1990, implying a roughly balanced Earth energy budget within −0.16 to 0.06 W m−2 over most of the latter half of the 20th century. However, the past three decades have seen a rapid acceleration in ocean warming, with the entire ocean warming from top to bottom at a rate of 0.63 ± 0.13 W m−2. These results suggest a delayed onset of a positive Earth energy imbalance relative to previous estimates, although large uncertainties remain.

Glacier fluctuations during the past millennium in Garibaldi Provincial Park, southern Coast Mountains, British Columbia

2007 ◽  
Vol 44 (9) ◽  
pp. 1215-1233 ◽  
Author(s):  
Johannes Koch ◽  
John J Clague ◽  
Gerald D Osborn
Keyword(s):  
British Columbia ◽  
Little Ice Age ◽  
Ice Age ◽  
Southern Coast ◽  
Coast Mountains ◽  
The Past ◽  
Glacier Fluctuations ◽  
Garibaldi Provincial Park ◽  
Provincial Park ◽  
Past Millennium

The Little Ice Age glacier history in Garibaldi Provincial Park (southern Coast Mountains, British Columbia) was reconstructed using geomorphic mapping, radiocarbon ages on fossil wood in glacier forefields, dendrochronology, and lichenometry. The Little Ice Age began in the 11th century. Glaciers reached their first maximum of the past millennium in the 12th century. They were only slightly more extensive than today in the 13th century, but advanced at least twice in the 14th and 15th centuries to near their maximum Little Ice Age positions. Glaciers probably fluctuated around these advanced positions from the 15th century to the beginning of the 18th century. They achieved their greatest extent between A.D. 1690 and 1720. Moraines were deposited at positions beyond present-day ice limits throughout the 19th and early 20th centuries. Glacier fluctuations appear to be synchronous throughout Garibaldi Park. This chronology agrees well with similar records from other mountain ranges and with reconstructed Northern Hemisphere temperature series, indicating global forcing of glacier fluctuations in the past millennium. It also corresponds with sunspot minima, indicating that solar irradiance plays an important role in late Holocene climate change.

Humidity variations spanning the ‘Little Ice Age’ from an upland lake in southwestern China

The Holocene ◽  
2019 ◽  
Vol 30 (2) ◽  
pp. 289-299
Author(s):  
Tingwei Zhang ◽  
Xiaoqiang Yang ◽  
Qiong Chen ◽  
Jaime L Toney ◽  
Qixian Zhou ◽  
...  
Keyword(s):  
Little Ice Age ◽  
Asian Monsoon ◽  
Activity Index ◽  
Ice Age ◽  
Western China ◽  
Southwestern China ◽  
Sunspot Activity ◽  
Precipitation Pattern ◽  
The Past ◽  
Westerly Jet

A number of archives that span the past ~2000 years suggest that recent variability in hydroclimatic conditions that are influenced by the Asian monsoon in China are unusual in the longer term context. However, the lack of high-resolution precipitation records over this period hampered our ability to characterize and constrain the forcing mechanism(s) of the recent humidity variations. Here, we present the ratio of hematite to goethite (Hm/Gt) derived from the semiquantitative evaluation of the diffuse reflectance spectroscopic analysis as a reliable and effective precipitation proxy to reconstruct the humidity variations during the past 1400 years deduced from Tengchongqinghai Lake sediments, southwestern China. Hm/Gt varied synchronously with variations of Chinese temperature reconstructed from the historical documents and sunspot activity index over the past 1400 years. Critical periodicities of ~450 and ~250 years show that solar activity is the dominant control on precipitation change on centennial scales. However, the relationship determined from Hm/Gt in this study contradicts the stalagmite δ18O interpretations from different regions of China, which exhibit a more complex precipitation pattern that is influenced by the strength of westerly jet in addition to the Asian monsoon. The increased westerly jet during the ‘Little Ice Age’ (LIA) caused a humid climate in southern China and dry conditions in northern and western China.

Indications for a North Atlantic ocean circulation regime shift at the onset of the Little Ice Age

2015 ◽  
Vol 45 (11-12) ◽  
pp. 3623-3633 ◽  
Author(s):  
C.-F. Schleussner ◽  
D. V. Divine ◽  
J. F. Donges ◽  
A. Miettinen ◽  
R. V. Donner
Keyword(s):  
Atlantic Ocean ◽  
Ocean Circulation ◽  
North Atlantic ◽  
Little Ice Age ◽  
Regime Shift ◽  
North Atlantic Ocean ◽  
Ice Age ◽  
Circulation Regime
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