Climate Feedbacks in the Alaskan Boreal Forest

2006 ◽  
Author(s):  
F. Stuart Chapin III ◽  
A. David McGuire
Keyword(s):  
Boreal Forest ◽  
Arctic Ocean ◽  
Fresh Water ◽  
Land Surface ◽  
Boreal Forests ◽  
Energy Exchange ◽  
Climate System ◽  
The Arctic ◽  
The Arctic Ocean ◽  
Forest Biome

The boreal forest biome occupies an area of 18.5 million km2, which is approximately 14% of the vegetated cover of the earth’s surface (McGuire et al. 1995b). North of 50°N, terrestrial interactions with the climate system are dominated by the boreal forest biome because of its large aerial extent (Bonan et al. 1992, Chapin et al. 2000b; Fig. 19.1). There are three major pathways through which the function and structure of boreal forests may influence the climate system: (1) water/energy exchange with the atmosphere, (2) the exchange of radiatively active gases with the atmosphere, and (3) delivery of fresh water to the Arctic Ocean. The exchange of water and energy has implications for regional climate that may influence global climate, while the exchange of radiatively active gases and the delivery of fresh water to the Arctic Ocean are processes that could directly influence climate at the global scale. In this chapter, we first discuss the current understanding of the role that boreal forests play in each of these pathways and identify key issues that remain to be explored. We then discuss the implications for the earth’s climate system of likely responses of boreal forests to various dimensions of ongoing global change. Most of the energy that heats the earth’s atmosphere is first absorbed by the land surface and then transferred to the atmosphere. The energy exchange properties of the land surface therefore have a strong direct influence on climate. Boreal forest differs from more southerly biomes in having a long period of snow cover, when white surfaces might be expected to reflect incoming radiation (high albedo) and therefore absorb less energy for transfer to the atmosphere. Observed winter albedo in the boreal forest varies between 0.11 (conifer stands) and 0.21 (deciduous stands; Betts and Ball 1997). This is much closer to the summer albedo (0.08–0.15) than to the winter albedo of tundra (0.6–0.8), which weather models had previously assumed to be appropriate for boreal forests. The incorporation of true boreal albedo into climate models led to substantial improvements in medium-range weather forecasting (Viterbo and Betts 1999).

scholarly journals Ice Lithologies and Structure of Ice Island Arlis II

1964 ◽  
Vol 5 (37) ◽  
pp. 17-38 ◽  
Author(s):  
David D. Smith
Keyword(s):  
Sea Ice ◽  
Arctic Ocean ◽  
Fresh Water ◽  
Structural Features ◽  
The Arctic ◽  
Glacial Ice ◽  
Water Ice ◽  
Central Block ◽  
The Arctic Ocean

AbstractIce island ARLIS II, which is adrift in the Arctic Ocean, is a 1.3 km. wide and 3.8 km. long fragment of shelf ice 12–25 m. thick, which preserves several structural features heretofore undescribed in ice. The island is composed of an irregular central block of foliated, locally debris-rich, grey glacial ice bordered in part by extensive areas of stratified bluish sea ice. The central block contains a series of narrow, elongate, sub-parallel dike-like septa of massive fresh-water ice and a large tongue-like body of tightly folded, coarse banded ice. Both the septa and the tongue cut across the foliation and debris zones of the grey ice.The margins of the central block are penetrated by a series of elongate, crudely wedge-shaped re-entrants occupied by salients of bluish sea ice. Two broad, arch-like plunging anticlines deform the stratified sea ice along one margin of the block.The foliation and debris zones in the glacial ice are relict features inherited from the source glacier. The septa formed as crevasse and basal fracture fills. Salients represent fills formed in the irregular re-entrants along the margins of the glacial ice mass. The tongue of tightly folded, banded ice represents an earlier generation salient deformed by compressive forces as the fill built up. The broad anticlines are apparently the result of warping in response to differential ablation but the small, tight plunging folds on their noses and limbs are probably the result of compressive forces.

scholarly journals Ice Lithologies and Structure of Ice Island Arlis II

1964 ◽  
Vol 5 (37) ◽  
pp. 17-38 ◽  
Author(s):  
David D. Smith
Keyword(s):  
Sea Ice ◽  
Arctic Ocean ◽  
Fresh Water ◽  
Structural Features ◽  
The Arctic ◽  
Glacial Ice ◽  
Water Ice ◽  
Central Block ◽  
The Arctic Ocean

Abstract Ice island ARLIS II, which is adrift in the Arctic Ocean, is a 1.3 km. wide and 3.8 km. long fragment of shelf ice 12–25 m. thick, which preserves several structural features heretofore undescribed in ice. The island is composed of an irregular central block of foliated, locally debris-rich, grey glacial ice bordered in part by extensive areas of stratified bluish sea ice. The central block contains a series of narrow, elongate, sub-parallel dike-like septa of massive fresh-water ice and a large tongue-like body of tightly folded, coarse banded ice. Both the septa and the tongue cut across the foliation and debris zones of the grey ice. The margins of the central block are penetrated by a series of elongate, crudely wedge-shaped re-entrants occupied by salients of bluish sea ice. Two broad, arch-like plunging anticlines deform the stratified sea ice along one margin of the block. The foliation and debris zones in the glacial ice are relict features inherited from the source glacier. The septa formed as crevasse and basal fracture fills. Salients represent fills formed in the irregular re-entrants along the margins of the glacial ice mass. The tongue of tightly folded, banded ice represents an earlier generation salient deformed by compressive forces as the fill built up. The broad anticlines are apparently the result of warping in response to differential ablation but the small, tight plunging folds on their noses and limbs are probably the result of compressive forces.

scholarly journals Freshwater in the Arctic Ocean 2010–2019

Ocean Science ◽  
2021 ◽  
Vol 17 (4) ◽  
pp. 1081-1102
Author(s):  
Amy Solomon ◽  
Céline Heuzé ◽  
Benjamin Rabe ◽  
Sheldon Bacon ◽  
Laurent Bertino ◽  
...  
Keyword(s):  
Sea Ice ◽  
Arctic Ocean ◽  
Moisture Transport ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Climate System ◽  
Arctic Climate ◽  
The Arctic ◽  
Beaufort Gyre ◽  
The Arctic Ocean

Abstract. The Arctic climate system is rapidly transitioning into a new regime with a reduction in the extent of sea ice, enhanced mixing in the ocean and atmosphere, and thus enhanced coupling within the ocean–ice–atmosphere system; these physical changes are leading to ecosystem changes in the Arctic Ocean. In this review paper, we assess one of the critically important aspects of this new regime, the variability of Arctic freshwater, which plays a fundamental role in the Arctic climate system by impacting ocean stratification and sea ice formation or melt. Liquid and solid freshwater exports also affect the global climate system, notably by impacting the global ocean overturning circulation. We assess how freshwater budgets have changed relative to the 2000–2010 period. We include discussions of processes such as poleward atmospheric moisture transport, runoff from the Greenland Ice Sheet and Arctic glaciers, the role of snow on sea ice, and vertical redistribution. Notably, sea ice cover has become more seasonal and more mobile; the mass loss of the Greenland Ice Sheet increased in the 2010s (particularly in the western, northern, and southern regions) and imported warm, salty Atlantic waters have shoaled. During 2000–2010, the Arctic Oscillation and moisture transport into the Arctic are in-phase and have a positive trend. This cyclonic atmospheric circulation pattern forces reduced freshwater content on the Atlantic–Eurasian side of the Arctic Ocean and freshwater gains in the Beaufort Gyre. We show that the trend in Arctic freshwater content in the 2010s has stabilized relative to the 2000s, potentially due to an increased compensation between a freshening of the Beaufort Gyre and a reduction in freshwater in the rest of the Arctic Ocean. However, large inter-model spread across the ocean reanalyses and uncertainty in the observations used in this study prevent a definitive conclusion about the degree of this compensation.

scholarly journals Freshwater in the Arctic Ocean 2010–2019

2020 ◽  
Author(s):  
Amy Solomon ◽  
Céline Heuzé ◽  
Benjamin Rabe ◽  
Sheldon Bacon ◽  
Laurent Bertino ◽  
...  
Keyword(s):  
Sea Ice ◽  
Arctic Ocean ◽  
Review Paper ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Climate System ◽  
Arctic Climate ◽  
The Arctic ◽  
Global Ocean ◽  
The Arctic Ocean

Abstract. The Arctic climate system is rapidly transitioning into a new regime with a reduction in the extent of sea ice, enhanced mixing in the ocean and atmosphere, and thus enhanced coupling within the ocean-ice-atmosphere system; these physical changes are leading to ecosystem changes in the Arctic Ocean. In this review paper, we assess one of the critically important aspects of this new regime, the variability of Arctic freshwater, which plays a fundamental role in the Arctic climate system by impacting ocean stratification and sea ice formation. Liquid and solid freshwater exports also affect the global climate system, notably by impacting the global ocean overturning circulation. In this review paper we assess to what extent observations during the 2010–2019 period are sufficient to estimate the Arctic freshwater budget with greater certainty than previous assessments and how this budget has changed relative to the 2000–2010 period. We include discussions of processes not included in previous assessments, such as run off from the Greenland Ice Sheet, the role of snow on sea ice, and vertical redistribution. We show that the trend in Arctic freshwater in the 2010s has stabilized relative to the 2000s due to an increased compensation between a freshening of the Beaufort Gyre and a reduction in freshwater in the Amerasian and Eurasian basins. Notably, the sea ice cover has become more seasonal and more mobile, the mass loss of the Greenland ice sheet has shifted from the western to the eastern part, and the import of subpolar waters into the Arctic has increased.

scholarly journals On large-scale shifts in the Arctic Ocean and sea-ice conditions during 1979−98

2001 ◽  
Vol 33 ◽  
pp. 545-550 ◽  
Author(s):  
W. Maslowski ◽  
D. C. Marble ◽  
W. Walczowski ◽  
A. J. Semtner
Keyword(s):  
Sea Ice ◽  
Arctic Ocean ◽  
Fresh Water ◽  
Ocean Circulation ◽  
Large Scale ◽  
Atlantic Water ◽  
The Arctic ◽  
Upper Ocean ◽  
Recent Climate ◽  
The Arctic Ocean

AbstractResults from a regional model of the Arctic Ocean and sea ice forced with realistic atmospheric data are analyzed to understand recent climate variability in the region. The primary simulation uses daily-averaged 1979 atmospheric fields repeated for 20 years and then continues with interannual forcing derived from the European Centre for Medium-range Weather Forecasts for 1979−98. An eastward shift in the ice-ocean circulation, fresh-water distribution and Atlantic Water extent has been determined by comparing conditions between the early 1980s and 1990s. A new trend is modeled in the late 1990s, and has a tendency to return the large-scale sea-ice and upper ocean conditions to their state in the early 1980s. Both the sea-ice and the upper ocean circulation as well as fresh-water export from the Russian shelves and Atlantic Water recirculation within the Eurasian Basin indicate that the Arctic climate is undergoing another shift. This suggests an oscillatory behavior of the Arctic Ocean system. Interannual atmospheric variability appears to be the main and sufficient driver of simulated changes. The ice cover acts as an effective dynamic medium for vorticity transfer from the atmosphere into the ocean.

scholarly journals Irtysh River Drove Arctic Sea Ice Expansion 3 Million Years Ago

Eos ◽  
2021 ◽  
Vol 102 ◽  
Author(s):  
David Shultz
Keyword(s):  
Sea Ice ◽  
Arctic Ocean ◽  
Fresh Water ◽  
Kara Sea ◽  
Arctic Sea Ice ◽  
The Arctic ◽  
Arctic Sea ◽  
The Arctic Ocean ◽  
Irtysh River ◽  
Earth’S Climate

The Siberian river’s creation caused a massive influx of fresh water into the Kara Sea and radically changed the Arctic Ocean and Earth’s climate.

Response/feedback of the Arctic Ocean in the Northern Hemisphere climate system: the sea-level joker

2020 ◽  
Author(s):  
Claude Hillaire-Marcel ◽  
Anne de Vernal ◽  
Yanguang Liu
Keyword(s):  
Sea Ice ◽  
Arctic Ocean ◽  
Northern Hemisphere ◽  
North Atlantic ◽  
Climate System ◽  
The Arctic ◽  
Bering Strait ◽  
The North ◽  
The Arctic Ocean ◽  
The Status

<p>The Arctic Ocean is a major player in the climate system of the Northern Hemisphere due to its role vs albedo, atmospheric pressure regimes, and thermohaline circulation. It shows large amplitude variability from millennial, to decadal and seasonal time scales. At millennial time scales, two drastically distinct regimes prevail primarily in relation with ocean volume and sea level (SL) changes: A modern like system, with a high SL when the Arctic Ocean shelves are submerged and Bering Strait is opened vs a glacial one, with a low SL, when shelves are emerged and partly glaciated and Bering Strait is closed. In the modern system, large submerged shelves result in high productivity, high sea-ice production rates and sea ice-rafting deposition in the Central Arctic. Moreover, a fully open Bering Strait, with SL at the present elevation, contributes about 40% of the freshwater budget of the Arctic Ocean (Woodgate & Aagaard, 2005, doi:10.1029/2004GL021747), and supports Si fluxes of about 20 kmol.s<sup>-1</sup> towards the Western Arctic (Torres-Valdés et al., 2013, doi:10.1002/jgrc.20063), thus impacting primary productivity. Under low SL conditions, the Arctic Ocean is linked exclusively to the North Atlantic, through practically a single gateway, that of Fram Strait. Sedimentation in the Central Arctic is then dominated ice-rafting deposition from icebergs, thus controlled by streaming and calving processes along surrounding ice sheets. Due to its shallowness (< 50 m), the Bering Strait gateway becomes effective at a very late stage of glacial to interglacial transitions but closes early during reverse climate trends. Sedimentary records from shelves North of Strait may provide information on the status of the gateway, so far, for the present interglacial. Clay minerals in cores from the northern Alaskan shelf (Ortiz et al., 2009, doi:10.1016/j.gloplacha.2009.03.020) and micropaleontological tracers from the Chukchi Sea southern shelf (present study) can be used to document the status of the gateway. Here, North Pacific microfossils transported by currents through the gateway demonstrate its full effectiveness at ca 6 ka BP, well after the insolation maximum of the early Holocene but when SL had reached its maximum postglacial elevation, with significant impacts on Arctic Ocean salinity, sea-ice cover and productivity.. This out-of-phase behavior of the Arctic Ocean may have impacted the North Atlantic and Northern Hemisphere climate system, as the openings and closings of Bering Strait constitute critical tipping points on this system, off out of phase with other parameters controlling more globally the climate of the Northern Hemisphere.</p>

scholarly journals Capturing How Fast the Arctic Ocean Is Gaining Fresh Water

Eos ◽  
2021 ◽  
Vol 102 ◽  
Author(s):  
Sarah Stanley
Keyword(s):  
Arctic Ocean ◽  
Fresh Water ◽  
Surface Waters ◽  
The Arctic ◽  
The Arctic Ocean ◽  
Arctic Surface

A new analysis suggests that models do not accurately capture how fresh Arctic surface waters mix with deeper waters, contributing to underestimation of Arctic surface freshening.

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