scholarly journals Investigating the Strength of the Indian Monsoons during Climate Extremes with Stable Isotope Records in Corals

2021 ◽  
Vol 1 (2) ◽  
Author(s):  
Hannah Varkey ◽  
Richard Mortlock ◽  
Cecilia Mchugh ◽  
Dhiman Mondal
Keyword(s):  
North Atlantic ◽  
Little Ice Age ◽  
Indian Monsoon ◽  
Climate Extremes ◽  
Relative Strength ◽  
Ice Age ◽  
Last Glacial Period ◽  
Salinity Changes ◽  
The North ◽  
The Last Glacial

The Indian monsoon affects the lives of over a billion inhabitants living in southern Asia via the hy-drological cycle. Agriculture on land and freshwater discharge into the ocean. This discharge and nutri-ent cycling are tied with the monsoon cycles that di-rectly impact society and the economy. Previous studies have demonstrated a strong connection be-tween the strength of the Indian monsoon and the cooling of the North Atlantic during climate ex-tremes, such as during the last glacial period 20,000 years ago, and the Little Ice Age (~1300-1870 A.D.). In our study, we compare the relative strength of the monsoon during two different climate states: the Lit-tle Ice Age (LIA) and the modern (2015) with proxy measurements obtained in surface corals from Saint Martin’s Island, Southeast Bangladesh. We used the oxygen-isotope 18O/16O ratio (δ18Oc) of coralline aragonite (CaCO3) to reconstruct changes in the δ18O of seawater (δ18Ow) attributed to freshening from monsoon rains. During both climate states, corals recorded large variations in δ18Oc (up to 2 parts per thousand or ‰). We attribute these changes, in part, to local salinity changes which are reflected by variability in δ18Ow from local riverine discharge. While our records only represent 5-year snapshots and may not be representative of the av-erage climate state, this data does not support that the monsoon was substantially weaker during the LIA compared to the modern. In this study, the coral records indicate subtle patterns of isotopic compo-sition as a function of precipitation and temperature variability, serving as a preliminary for further study through longer records lasting a century. Beyond this, it would better our understanding of interac-tions between extremes in temperature and climate systems.

scholarly journals Bunker Cave stalagmites: an archive for central European Holocene climate variability

2012 ◽  
Vol 8 (3) ◽  
pp. 1687-1720 ◽  
Author(s):  
J. Fohlmeister ◽  
A. Schröder-Ritzrau ◽  
D. Scholz ◽  
C. Spötl ◽  
D. F. C. Riechelmann ◽  
...  
Keyword(s):  
Climate Variability ◽  
North Atlantic ◽  
Little Ice Age ◽  
Ice Age ◽  
Holocene Climate ◽  
Central European ◽  
The North ◽  
The North Atlantic ◽  
Meteoric Precipitation ◽  
Precipitation And Temperature

Abstract. Holocene climate was characterised by variability on multi-centennial to multi-decadal time scales. In central Europe, these fluctuations were most pronounced during winter. Here we present a new record of past winter climate variability for the last 10.8 ka based on four speleothems from Bunker Cave, Western Germany. Due to its central European location, the cave site is particularly well suited to record changes in precipitation and temperature in response to changes in the North Atlantic realm. We present high resolution records of δ18O, δ13C values and Mg/Ca ratios. We attribute changes in the Mg/Ca ratio to variations in the meteoric precipitation. The stable C isotope composition of the speleothems most likely reflects changes in vegetation and precipitation and variations in the δ18O signal are interpreted as variations in meteoric precipitation and temperature. We found cold and dry periods between 9 and 7 ka, 6.5 and 5.5 ka, 4 and 3 ka as well as between 0.7 to 0.2 ka. The proxy signals in our stalagmites compare well with other isotope records and, thus, seem representative for central European Holocene climate variability. The prominent 8.2 ka event and the Little Ice Age cold events are both recorded in the Bunker cave record. However, these events show a contrasting relationship between climate and δ18O, which is explained by different causes underlying the two climate anomalies. Whereas the Little Ice Age is attributed to a pronounced negative phase of the North Atlantic Oscillation, the 8.2 ka event was triggered by cooler conditions in the North Atlantic due to a slowdown of the Thermohaline Circulation.

scholarly journals Tree-ring radiocarbon reveals reduced solar activity during Younger Dryas cooling

2020 ◽  
Author(s):  
Adam Sookdeo ◽  
Bernd Kromer ◽  
Florian Adolphi ◽  
Jürg Beer ◽  
Nicolas Brehm ◽  
...  
Keyword(s):  
Solar Activity ◽  
Tree Ring ◽  
North Atlantic ◽  
Little Ice Age ◽  
Ice Core ◽  
Younger Dryas ◽  
Ice Age ◽  
The North ◽  
Long Duration ◽  
Clear Sign

<p>The Younger Dryas stadial (YD) was a return to glacial-like conditions in the North Atlantic region that interrupted deglacial warming around 12900 cal BP (before 1950 AD). Terrestrial and marine records suggest this event was initiated by the interruption of deep-water formation arising from North American freshwater runoff, but the causes of the millennia-long duration remain unclear. To investigate the solar activity, a possible YD driver, we exploit the cosmic production signals of tree-ring radiocarbon (<sup>14</sup>C) and ice-core beryllium-10 (<sup>10</sup>Be). Here we present the highest temporally resolved dataset of <sup>14</sup>C measurements (n = 1558) derived from European tree rings that have been accurately extended back to 14226 cal BP (±8, 2-σ), allowing precise alignment of ice-core records across this period. We identify a substantial increase in <sup>14</sup>C and <sup>10</sup>Be production starting at 12780 cal BP is comparable in magnitude to the historic Little Ice Age, being a clear sign of grand solar minima. We hypothesize the timing of the grand solar minima provides a significant amplifying factor leading to the harsh sustained glacial-like conditions seen in the YD.</p>

Cuban stalagmite suggests relationship between Caribbean precipitation and the Atlantic Multidecadal Oscillation during the past 1.3 ka

The Holocene ◽  
2012 ◽  
Vol 22 (12) ◽  
pp. 1405-1412 ◽  
Author(s):  
Claudia Fensterer ◽  
Denis Scholz ◽  
Dirk Hoffmann ◽  
Christoph Spötl ◽  
Jesús M Pajón ◽  
...  
Keyword(s):  
North Atlantic ◽  
Little Ice Age ◽  
Rainfall Intensity ◽  
Thermohaline Circulation ◽  
Atlantic Multidecadal Oscillation ◽  
Ice Age ◽  
The Past ◽  
The North ◽  
Southward Shift ◽  
The North Atlantic

Here we present the first high-resolution δ18O record of a stalagmite from western Cuba. The record reflects precipitation variability in the northwestern Caribbean during the last 1.3 ka and exhibits a correlation to the Atlantic Multidecadal Oscillation (AMO). This suggests a relationship between Caribbean rainfall intensity and North Atlantic sea-surface temperature (SST) anomalies. A potential mechanism for this relationship may be the strength of the Thermohaline Circulation (THC). For a weaker THC, lower SSTs in the North Atlantic possibly lead to a southward shift of the Intertropical Convergence Zone and drier conditions in Cuba. Thus, this Cuban stalagmite records drier conditions during cold phases in the North Atlantic such as the ‘Little Ice Age’. This study contributes to the understanding of teleconnections between North Atlantic SSTs and northern Caribbean climate variability during the past 1.3 ka.

scholarly journals Late Holocene climate variability in the southwestern Mediterranean region: an integrated marine and terrestrial geochemical approach

2010 ◽  
Vol 6 (5) ◽  
pp. 1655-1683 ◽  
Author(s):  
C. Martín-Puertas ◽  
F. Jiménez-Espejo ◽  
F. Martínez-Ruiz ◽  
V. Nieto-Moreno ◽  
M. Rodrigo ◽  
...  
Keyword(s):  
Climate Variability ◽  
North Atlantic ◽  
Little Ice Age ◽  
Mediterranean Region ◽  
Late Holocene ◽  
Western Mediterranean ◽  
Warm Period ◽  
Ice Age ◽  
The North ◽  
The North Atlantic

Abstract. A combination of marine (Alboran Sea cores, ODP 976 and TTR 300 G) and terrestrial (Zoñar Lake, Andalucia, Spain) paleoclimate information using geochemical proxies provides a high resolution reconstruction of climate variability and human influence in southwestern Mediterranean region for the last 4000 years at inter-centennial resolution. Proxies respond to changes in precipitation rather than temperature alone. Our archive documents a succession of dry and wet periods coherent with the North Atlantic climate signal. Drier stages occurred prior to 2.7 cal ka BP, well-correlated with the global aridity crisis of the third-millennium BC, and during the Medieval Warm Period (1.4–0.7 cal ka BP). Wetter conditions prevailed from 2.7 to 1.4 cal ka BP and after the Medieval Warm Period and the onset of the Little Ice Age. Hydrological signatures during the Little Ice Age are highly variable but consistent with more humidity that the period before. Additionally, Pb anomalies in sediments at the end of Bronze Age suggest anthropogenic pollution earlier than the Roman Empire development in the Iberian Peninsula. The evolution of the climate in the study area during the Late Holocene confirms the see-saw pattern previously shown between eastern and western Mediterranean regions and suggests a higher influence of the North Atlantic dynamics in the western Mediterranean.

scholarly journals The origin of glacial alpine landscape in Tröllaskagi Peninsula (North Iceland)

2016 ◽  
Vol 42 (2) ◽  
pp. 341 ◽  
Author(s):  
N. Andrés ◽  
L. M. Tanarro ◽  
J. M. Fernández ◽  
D. Palacios
Keyword(s):  
North Atlantic ◽  
Little Ice Age ◽  
Ice Age ◽  
Important Advance ◽  
North Central ◽  
The North ◽  
Significant Difference ◽  
Rock Glaciers ◽  
Basalt Plateau ◽  
Tertiary Basalt

The Tröllaskagi peninsula is located in north central Iceland, between meridians 19º30’W and 18º10’W , limited by Skagafjödur fiord to the west and the Eyjafjödur fiord to the east, jutting out into the North Atlantic to latitude 66º12’N and linked to the central Icelandic highlands to the south. The peninsula is a Tertiary basalt plateau topped by flat summits with altitudes of 1000-1500 m, intensely dissected by the drainage network. The aim of this present study is to synthesize the recent advances in our understanding of the landscape and its dynamics in the Tröllaskagi peninsula and find the origin of its significant difference from the rest of Iceland. Results of the most recent research suggest the situation of Tröllaskagi as ice-free, delimited by the two great glacial outlets flowing down from the Icelandic Ice Sheet through the Skagafjödur and Eyjafjödur fiords, from at least the Oldest Dryas to the end of the Early Preboreal. Inland in Tröllaskagi, the glaciers formed in the north-facing cirques without losing their alpine characteristics during the Late Pleistocene and Holocene. The advances of these glaciers during the Oldest, Older and Youngest Dryas and the Early Preboreal were only a few hundred metres greater than the most important advance in the second half of the Holocene, during the Little Ice Age. Only a few of these glaciers remained debris-free and are sensitive to the minor climate oscillations. The rest, due to the important geomorphological activity on their walls, developed into debris-covered and rock glaciers and lost this significant dynamism.

scholarly journals Radiocarbon/Tree-Ring Calibration, Solar Activity, and Upwelling of Ocean Water

Radiocarbon ◽  
2004 ◽  
Vol 46 (2) ◽  
pp. 987-995 ◽  
Author(s):  
F B Knox ◽  
B G McFadgen
Keyword(s):  
Solar Activity ◽  
Tree Ring ◽  
North Atlantic ◽  
Little Ice Age ◽  
Ice Age ◽  
Calibration Data ◽  
Ocean Water ◽  
Smooth Curves ◽  
The North ◽  
Oceanic Upwelling

Least-squares fitted smooth curves to radiocarbon versus tree-ring calibration data for the period AD 1140 to 1950 are compared with climatic warming and cooling of the North Atlantic (Little Ice Age), and with recorded sunspot numbers over the period AD 1670 to 1950.Calibration curves from different parts of the globe are not identical, and appear to be determined by a combination of variable solar activity and variable oceanic upwelling of 14C-depleted water, with the variable upwelling itself partly determined by solar activity.

Bivalves indicate that the North Atlantic was under stress before the onset of the Little Ice Age

2021 ◽  
Author(s):  
Beatriz Arellano Nava ◽  
Paul R. Halloran ◽  
Chris A. Boulton ◽  
Timothy M. Lenton
Keyword(s):  
Marine Environment ◽  
North Atlantic ◽  
Little Ice Age ◽  
Stable State ◽  
Volcanic Eruptions ◽  
Ice Age ◽  
Last Millennium ◽  
The North ◽  
Growth Increments ◽  
Negative Feedbacks

<p>The last millennium was characterised by a cooling from the Medieval Warm Period into the Little Ice Age. While strong volcanic eruptions could have triggered the onset of the Little Ice Age by reducing solar irradiance, modelling experiments suggest that it was amplified and maintained by sea ice-ocean feedbacks, including a potential abrupt weakening of the subpolar gyre. The weakening of negative feedbacks that maintain a system in a stable state, prior to an abrupt transition, can be detected as an increase in temporal autocorrelation and variability. Here we use an annually-resolved and absolutely dated shell-derived record from the North Icelandic Shelf that spans the last millennium, to detect such a loss of resilience in the marine environment leading up to the Little Ice Age transition. We find a significant increase in autocorrelation and variance in bivalve growth increments and oxygen isotopes before the transition, providing evidence consistent with loss of stability in the marine environment. This supports the idea that internal feedbacks played an important role in the Little Ice Age onset.</p>

scholarly journals Bunker Cave stalagmites: an archive for central European Holocene climate variability

2012 ◽  
Vol 8 (5) ◽  
pp. 1751-1764 ◽  
Author(s):  
J. Fohlmeister ◽  
A. Schröder-Ritzrau ◽  
D. Scholz ◽  
C. Spötl ◽  
D. F. C. Riechelmann ◽  
...  
Keyword(s):  
Climate Variability ◽  
North Atlantic ◽  
Little Ice Age ◽  
Ice Age ◽  
Holocene Climate ◽  
Central European ◽  
The North ◽  
The North Atlantic ◽  
Meteoric Precipitation ◽  
Precipitation And Temperature

Abstract. Holocene climate was characterised by variability on multi-centennial to multi-decadal time scales. In central Europe, these fluctuations were most pronounced during winter. Here we present a record of past winter climate variability for the last 10.8 ka based on four speleothems from Bunker Cave, western Germany. Due to its central European location, the cave site is particularly well suited to record changes in precipitation and temperature in response to changes in the North Atlantic realm. We present high-resolution records of δ18O, δ13C values and Mg/Ca ratios. Changes in the Mg/Ca ratio are attributed to past meteoric precipitation variability. The stable C isotope composition of the speleothems most likely reflects changes in vegetation and precipitation, and variations in the δ18O signal are interpreted as variations in meteoric precipitation and temperature. We found cold and dry periods between 8 and 7 ka, 6.5 and 5.5 ka, 4 and 3 ka as well as between 0.7 and 0.2 ka. The proxy signals in the Bunker Cave stalagmites compare well with other isotope records and, thus, seem representative for central European Holocene climate variability. The prominent 8.2 ka event and the Little Ice Age cold events are both recorded in the Bunker Cave record. However, these events show a contrasting relationship between climate and δ18O, which is explained by different causes underlying the two climate anomalies. Whereas the Little Ice Age is attributed to a pronounced negative phase of the North Atlantic Oscillation, the 8.2 ka event was triggered by cooler conditions in the North Atlantic due to a slowdown of the thermohaline circulation.

scholarly journals The Atmosphere’s Response to the Ice Sheets of the Last Glacial Maximum

1990 ◽  
Vol 14 ◽  
pp. 32-38 ◽  
Author(s):  
Kerry H. Cook
Keyword(s):  
Atlantic Ocean ◽  
North Atlantic ◽  
North Atlantic Ocean ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Ice Age ◽  
Laurentide Ice Sheet ◽  
Stationary Waves ◽  
The North ◽  
The Last Glacial

This paper discusses some modeling results that indicate how the atmospheric response to the topography of the continental ice of the Last Glacial Maximum (LGM) may be related to the cold North Atlantic Ocean of that time. Broccoli and Manabe (1987) used a three-dimensional general circulation model (GCM) of the atmosphere coupled with a fixed-depth, static ocean mixed-layer model with ice-age boundary conditions to investigate the individual influences of the CLIMAP ice sheets, snow-free land albedos, and reduced atmospheric CO2 concentrations. They found that the ice sheets are the most influential of the ice-age boundary conditions in modifying the northern hemisphere climate, and that the presence of continental ice sheets alone leads to cooling over the North Atlantic Ocean. One approach for extending these GCM results is to consider the stationary waves generated by the ice sheets. Cook and Held (1988) showed that a linearized, steady-state, primitive equation model can give a reasonable simulation of the GCM’s stationary waves forced by the Laurentide ice sheet. The linear model analysis suggests that the mechanical effect of the changed slope of the surface, and not changes in the diabatic heating (e.g. the high surface albedos) or time-dependent transports that necessarily accompany the ice sheet in the GCM, is largely responsible for the ice sheet’s influence. To obtain the ice-age stationary-wave simulation, the linear model must be linearized about the zonal mean fields from the GCM’s ice-age climate. This is the case because the proximity of the cold polar air to the region of adiabatic heating on the downslope of the Laurentide ice sheet is an important factor in determining the stationary waves. During the ice age, cold air can be transported southward to balance this downslope heating by small perturbations in the meridional wind, consistent with linear theory. Since the meridional temperature gradient is more closely related to the surface albedo (ice extent) than to the ice volume, this suggests a mechanism by which changes in the stationary waves and, therefore, their cooling influence at low levels over the North Atlantic Ocean, can occur on time scales faster than those associated with large changes in continental ice volume.

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