Global biomes and ecozones – Conceptual and spatial communalities and discrepancies

Various facets of global changes and related problems and challenges are asking for sound impact assessments and corresponding coping strategies. The human impact on nature is a major driver of biodiversity loss and restricted ecosystem functioning and services. Assessing such global changes is often done by using biomes as benchmarks. However, even if the wording and terminology seem common sense (‘tropical rain forest’, ‘steppe’, ‘boreal forest’) global biome units and maps deviate in many ways. This is well justified by their individual intention, expert opinions, disciplinary background, and methodology of creation. A closer look reveals linkages between spatial accordance and common origin in climate classifications and maps. Their original influence, however, is rarely evident. In consequence, it is difficult if not impossible for users to realize and understand differences in these global maps. Furthermore, it is difficult to accept the fact that there is no common standard for global biomes. Even more surprising is the fact that some approaches are uncritically taken for common sense and are perpetuated over decades. This study aims to review established global biome concepts. Regions that are consistently assigned to comparable types of biomes shall be detected and also regions where ambiguity exists. For this purpose, we shortly review the history of existing concepts and the generic relations between them. Biomes, ecozones and climate classifications are considered. We digitized the most prominent biome classifications. Spatial match and mismatch between concepts were analyzed globally. We detect areas of spatial agreement and regions with ambiguous classifications. A clustering approach including 287 individual biomes originating from 12 established global biome concepts and their classifications/units revealed 12 terrestrial biome clusters among which 8 can be assigned to terrestrial ecological units. One cluster on ice caps adds to this. And finally, 3 clusters represent rather transition zones (ecotones), high mountain plateaus or are of minor areal extent. The spatial arrangement of these emerging clusters is displayed on a global map. Additionally, regions of uncertainty related to class assignment were identified. Those primarily occur in the vicinity of mountainous regions. The findings of this study should be seen as a work in progress and as a basis for further optimization of global biome concepts.

Simulation of the Global Coupled Climate/Ice Sheet System over Millennial Timescales

<p>Ice sheets are important components of the Earth system that are expected to respond strongly to anthropogenic forcing of climate. The aim of this work is to use numerical climate and ice sheet modelling to identify and understand the millennial-scale interaction between the Antarctic and Greenland Ice Sheets (AIS and GIS) and global climate. An initial modelling effort evaluated the response of ice shelves and ice sheets to future CO2 emission scenarios by quantifying the duration and magnitude of summer melt periods. A temperature threshold based on positive degree days was applied to bias-corrected University of Victoria Earth System Climate Model (UVic ESCM) output spanning 1000 years into the future. The simulations indicated that an increase in summer melting over most of the GIS, the Ross and Ronne-Filchner ice shelves, and large sections of the West Antarctic Ice Sheet (where little present-day ablation occurs) could occur if future emissions are not curtailed. This initial work highlighted the need to assess the dynamic response of ice sheets to climate change. I therefore developed an ice sheet/climate model comprised of the UVic ESCM and the Pennsylvania State University Ice Sheet Model. Coupling these models required development of new techniques, including subgrid-scale energy balance calculations that incorporate a surface air temperature (SAT) model bias correction procedure. In testing the model, I found that climate model SAT bias, meltwater refreezing and albedo variations play an important role in simulated ice sheet evolution, particularly as more of the ice surface experiences melting conditions. The model realistically reproduced the AIS and GIS, and captured the surface mass balance (SMB) distributions for both ice sheets well for the present day, including narrow GIS ablation zones. The newly developed model was used to carry out a suite of experiments designed to assess the behavior of the GIS under elevated-CO2 conditions. A deglacial SMB-based GIS stability threshold was identified between 3-4x preindustrial atmospheric levels (PAL) of CO2. Below the threshold, GIS retreat still occurred but the ice ultimately stabilized in a ‘reduced ice sheet’ configuration, while at CO2 >= 4x PAL CO2, ice retreated to mountain ice caps. Ice sheet inception simulations indicated that above 4x PAL CO2, ice growth was limited, while at 4x PAL CO2 ice was able to reach the eastern Greenland coastline. Between 2-3x PAL CO2, separate ice caps in the southern and eastern mountains coalesced and exported ice onto the lowland plains. Large-scale ice sheet growth was limited until 1-2x PAL CO2. GIS ice loss increased with greater cumulative CO2 emissions in transient simulations. However, the ice sheet was able to briefly overshoot the CO2 stability threshold without experiencing drastic ice retreat due to the long response time of the simulated GIS relative to the rate of deep ocean carbon uptake. Finally, several model experiments were carried out using the coupled model to examine the impact of ocean melt-driven AIS retreat on the oceanic circulation and structure. This retreat produced freshwater fluxes to the Southern Ocean that were of the same magnitude (and initially greater) than the background continental flux, and continued for 3000 years after the initial shift to high-melt conditions. The Ross and Weddell Seas became productive sea ice export regions, which resulted in higher salinities in these seas and very low ocean temperatures. Enhanced sea ice export and melt in the open Southern Ocean contributed to a slight shallowing and weakening of the North Atlantic Deepwater circulation cell, that would reinforce predicted trends expected as a result of future anthropogenic CO2 emissions.</p>

Simulation of the Global Coupled Climate/Ice Sheet System over Millennial Timescales

<p>Ice sheets are important components of the Earth system that are expected to respond strongly to anthropogenic forcing of climate. The aim of this work is to use numerical climate and ice sheet modelling to identify and understand the millennial-scale interaction between the Antarctic and Greenland Ice Sheets (AIS and GIS) and global climate. An initial modelling effort evaluated the response of ice shelves and ice sheets to future CO2 emission scenarios by quantifying the duration and magnitude of summer melt periods. A temperature threshold based on positive degree days was applied to bias-corrected University of Victoria Earth System Climate Model (UVic ESCM) output spanning 1000 years into the future. The simulations indicated that an increase in summer melting over most of the GIS, the Ross and Ronne-Filchner ice shelves, and large sections of the West Antarctic Ice Sheet (where little present-day ablation occurs) could occur if future emissions are not curtailed. This initial work highlighted the need to assess the dynamic response of ice sheets to climate change. I therefore developed an ice sheet/climate model comprised of the UVic ESCM and the Pennsylvania State University Ice Sheet Model. Coupling these models required development of new techniques, including subgrid-scale energy balance calculations that incorporate a surface air temperature (SAT) model bias correction procedure. In testing the model, I found that climate model SAT bias, meltwater refreezing and albedo variations play an important role in simulated ice sheet evolution, particularly as more of the ice surface experiences melting conditions. The model realistically reproduced the AIS and GIS, and captured the surface mass balance (SMB) distributions for both ice sheets well for the present day, including narrow GIS ablation zones. The newly developed model was used to carry out a suite of experiments designed to assess the behavior of the GIS under elevated-CO2 conditions. A deglacial SMB-based GIS stability threshold was identified between 3-4x preindustrial atmospheric levels (PAL) of CO2. Below the threshold, GIS retreat still occurred but the ice ultimately stabilized in a ‘reduced ice sheet’ configuration, while at CO2 >= 4x PAL CO2, ice retreated to mountain ice caps. Ice sheet inception simulations indicated that above 4x PAL CO2, ice growth was limited, while at 4x PAL CO2 ice was able to reach the eastern Greenland coastline. Between 2-3x PAL CO2, separate ice caps in the southern and eastern mountains coalesced and exported ice onto the lowland plains. Large-scale ice sheet growth was limited until 1-2x PAL CO2. GIS ice loss increased with greater cumulative CO2 emissions in transient simulations. However, the ice sheet was able to briefly overshoot the CO2 stability threshold without experiencing drastic ice retreat due to the long response time of the simulated GIS relative to the rate of deep ocean carbon uptake. Finally, several model experiments were carried out using the coupled model to examine the impact of ocean melt-driven AIS retreat on the oceanic circulation and structure. This retreat produced freshwater fluxes to the Southern Ocean that were of the same magnitude (and initially greater) than the background continental flux, and continued for 3000 years after the initial shift to high-melt conditions. The Ross and Weddell Seas became productive sea ice export regions, which resulted in higher salinities in these seas and very low ocean temperatures. Enhanced sea ice export and melt in the open Southern Ocean contributed to a slight shallowing and weakening of the North Atlantic Deepwater circulation cell, that would reinforce predicted trends expected as a result of future anthropogenic CO2 emissions.</p>

Late Pleistocene and early Holocene sea-level history and glacial retreat interpreted from shell-bearing marine deposits of southeastern Alaska, USA

We leverage a data set of &gt;720 shell-bearing marine deposits throughout southeastern Alaska (USA) to develop updated relative sea-level curves that span the past ~14,000 yr. This data set includes site location, elevation, description when available, and 436 14C ages, 45 of which are published here for the first time. Our sea-level curves suggest a peripheral forebulge developed west of the retreating Cordilleran Ice Sheet (CIS) margin between ca. 17,000 and 10,800 calibrated yr B.P. By 14,870 ± 630 to 12,820 ± 340 cal. yr B.P., CIS margins had retreated from all of southeastern Alaska’s fjords, channels, and passages. At this time, isolated or stranded ice caps existed on the islands, with alpine or tidewater glaciers in many valleys. Paleoshorelines up to 25 m above sea level mark the maximum elevation of transgression in the southern portion of the study region, which was achieved by 11,000 ± 390 to 10,500 ± 420 cal. yr B.P. The presence of Pacific sardine (Sardinops sagax) and the abundance of charcoal in sediments that date between 11,000 ± 390 and 7630 ± 90 cal. yr B.P. suggest that both ocean and air temperatures in southeastern Alaska were relatively warm in the early Holocene. The sea-level and paleoenvironmental reconstruction presented here can inform future investigations into the glacial, volcanic, and archaeological history of southeastern Alaska.

DYNAMIC RESPONSE OF PHOTOPOLYMER RESINS CORES FOR NAVAL APPLICATIONS IN EXTREME ENVIRONMENTS

Due to the melting of polar ice caps, large deposits of natural resources are becoming more readily available, leading to an increase in arctic naval exploration. Naval vessels and ship hulls must be built with lightweight structures, such as sandwich composites, to increase the ship’s fuel efficiency. However, identifying new material choices that can withstand the harsh Arctic environments is crucial for the survivability and safety of personnel and structures. This study investigates the potential of photopolymer resins through additive manufacturing as a lightweight sandwich composite core material. The thermo-mechanical properties of this resin were evaluated using: tensile, flexural, and compressive tests according to the ASTM Standards D638, D695, and D790, respectively. Tests were conducted at room temperature (23 C) and arctic temperature (-60 C). The experimental data will be used as an input for high-fidelity finite element (FE) simulations with the software ABAQUS. From the performed tests, the photopolymer exhibited isotropic behavior at both room (RT) and Arctic temperatures. Preliminary quasi-static results for “Durable Resin” at AT showed an increase of ~300% in its tensile, flexural, and compressive modulus and an increase of ~300% in its tensile and flexural strength and ~100% in its compressive strength when compared to the same resin at RT. The finite element analysis models showed good agreement with the experimental results. Zackery Nieto, The University of Texas at El Paso, 500 W. University Ave, El Paso,

Modeling of hot-point drilling in ice

Hot-point drills have been widely used for drilling boreholes in glaciers, ice caps and ice sheets. A hot-point drill melts ice through the thermal head at its bottom end. Penetration occurs through a close-contact melting (CCM) process, in which the ice is melted, and the meltwater is squeezed out by the exerted force applied on the thermal head. During the drilling, a thin water film is formed to separate the thermal head from the surrounding ice. For the hot-point drill, the rate of penetration (ROP) is influenced by several variables, such as thermal head shape, buoyancy corrected force (BCF), thermal head power (or temperature) and ice temperature. In this study, we developed a model to describe the CCM process, where a constant power or temperature on the working surface of a thermal head is assumed. The model was developed using COMSOL Multiphysics 5.3a software to evaluate the effects of different variables on the CCM process. It was discovered that the effect of thermal head shape and the cone angle of conical thermal head on ROP is less significant, whereas the increase in the BCF and the power (or temperature) of the thermal head can continuously enhance the ROP.

Geodetic Mass Balance of the South Shetland Islands Ice Caps, Antarctica, from Differencing TanDEM-X DEMs

Although the glaciers in the Antarctic periphery currently modestly contribute to sea level rise, their contribution is projected to increase substantially until the end of the 21st century. The South Shetland Islands (SSI), located to the north of the Antarctic Peninsula, are lacking a geodetic mass balance calculation for the entire archipelago. We estimated its geodetic mass balance over a 3–4-year period within 2013–2017. Our estimation is based on remotely sensed multispectral and interferometric SAR data covering 96% of the glacierized areas of the islands considered in our study and 73% of the total glacierized area of the SSI archipelago (Elephant, Clarence, and Smith Islands were excluded due to data limitations). Our results show a close to balance, slightly negative average specific mass balance for the whole area of −0.106 ± 0.007 m w.e. a−1, representing a mass change of −238 ± 12 Mt a−1. These results are consistent with a wider scale geodetic mass balance estimation and with glaciological mass balance measurements at SSI locations for the same study period. They are also consistent with the cooling trend observed in the region between 1998 and the mid-2010s.