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Increasing mass loss from the Antarctic Ice Sheet has contributed to recent acceleration in the rate of global mean sea-level rise (SLR). Its full SLR potential is ~58 m, and its future contribution remains highly uncertain. The flow of Antarctica’s grounded ice into the ocean, and thus its contribution to SLR, is regulated by buttressing from floating ice shelves. Ice-shelf mass loss can reduce this buttressing effect. In this dissertation, I used satellite and airborne remote sensing data to explore three processes by which the ocean drives mass change on Antarctica’s large Ross Ice Shelf (RIS).First, I compared RIS thicknesses estimated from satellite laser altimetry and ROSETTA-Ice airborne radar data to identify a potential area of basal marine-ice accretion (i.e., local mass gain) in the ice-shelf interior. Large uncertainties prevent a definitive conclusion; reducing uncertainties will require additional measurements of ice-column density and firn properties. Second, I showed that airborne radar thickness profiles capture near-front thinning of RIS associated with basal melting by seasonally warmed upper-ocean water.Finally, I investigated the bending of the RIS front due to buoyancy created by the melting-related development of a submerged bench of ice, a mechanism that may lead to mass loss by calving of small icebergs. Profiles of the ice-shelf surface height from two satellite laser altimetry missions (ICESat, 2003–2009; and ICESat-2, 2018–present) reveal that this bending is larger on the eastern section of the RIS front, reflecting along-front variability in near-front ice thickness and ocean conditions. I also found that the surface deformation increased overall between 2018 and 2022. Between the two satellite mission periods, these surface structures grew along sections of the RIS front that experienced large calving events in the early 2000s.Taken together, these studies demonstrate that important mass-balance processes at the interface of ice shelf and ocean occur at small spatial scales that can only be resolved over large areas by high-resolution satellite and airborne sensors. Better understanding of these processes will require a combination of improved data density and models that correctly represent ocean properties and ice mechanical processes.

Late Holocene climate variability and coastal change of the Yucatan Peninsula, MexicoKyle Houston BroachThe following dissertation contains three studies that use sediment cores to reconstruct past changes in the climate and environment of a tropical lagoon system. These studies provide insight into past droughts and coastal change during geologically recent climate variability and sea-level rise by investigating relationships between geochemical and biological parameters sensitive to different processes occurring on the coast of the Yucatan Peninsula, Mexico.Chapter one is a foraminiferal fossil record reconstruction of the Celestun Lagoon environment, assessing ecologic response to a change in lagoon salinity and vegetation over the Late Holocene (5,300 years to present). The record and modern environment suggests foraminiferal community composition changes predictably with salinity, but lagoon salinity decreased primarily from restriction of seawater input to the lagoon, and hence reduced mixing between groundwater and seawater, rather than climate-induced increase of groundwater discharge, though climate is a secondary control. The cause of reduced mixing appears to be accumulation of barrier islands and sand spits that progressively isolated the northern lagoon, reducing mixing between groundwater discharge and seawater and shifting the environment from an open marine coast to estuarine lagoon. The transition was accompanied by expansion of the mangrove forest fringing the coastline. Superimposed on this trend, excursions of foraminifera taxa signify higher salinity coinciding with regionally dry periods and indicate that climate is a second-order control on lagoon mean salinity.Chapter two is a more detailed paleosalinity reconstruction where relations between modern lagoon salinity and both trace metals and isotopes in foraminiferal tests are applied to samples from cores collected along a transect from the northern to southern lagoon. The benthic species Ammonia parkinsoniana is used due to its abundance throughout the lagoon, and paleosalinity tracers recorded in A. parkinsoniana calcite tests are the elemental ratios Sr/Ca, and Ba/Ca and isotopes δ18O and 87Sr/86Sr. Ba/Ca ratios exhibit the highest correlation with salinity while δ18O and 87Sr/86Sr indicate two types of groundwater discharge to the lagoon—a fresh and a brackish source. A mixing model constructed from δ18O and 87Sr/86Sr show that long-term decrease in salinity was due to increased proportions of the brackish groundwater endmember—consistent with the Chapter 1—and decreases in the freshwater endmember coincide with major dry periods in the Yucatan recorded in other paleoclimate archives of the region. Furthermore, sedimentation rates increase briefly at 3,400 and 2,000 years ago, time periods characterized by large-scale reorganization of atmospheric and oceanic currents in the North Atlantic with atmospheric teleconnections to tropical climate. These increases in accumulation rate are interpreted as periods of rapid barrier island accumulation as trade winds and the Loop Current weaken in the Gulf of Mexico and deposit sediments during longshore drift. Chapter two suggests that atmospheric patterns resulting in drought in the Yucatan Peninsula also result in rapid sedimentation and apparent decrease in salinity in coastal lagoons, thus demonstrating the value of a multi-proxy approach in reconstructing paleoenvironmental history in dynamic coastal environments.Chapter three contributes data and a new hypothesis to the growing body of literature on the boron isotope system. The boron isotope ratio 11B/10B records pH of ambient water in the carbonate shells, proving to be a powerful tool in reconstructing past ocean acidification and atmospheric carbon dioxide concentrations. However, δ11B has not previously been used as a proxy for low-pH spring water discharge. In Celestun Lagoon, boron measurements in A. parkinsoniana are characterized by high variability both in surface sediments along the lagoon and in downcore samples and exhibit weak but significant relationships with the paleosalinity proxies 87Sr/86Sr and Ba/Ca and with the vegetation proxy δ13C. Lower pH caused by respiration of organic matter, recorded in δ13C of calcite, appears to contribute to δ11B variability, yet mean δ11B values of calcite reflect calculated δ11B values of borate based on present understanding of boron systematics, thus indicating that spring discharge exerts a first-order control on lagoon pH and δ11B recorded in foraminifera. This finding is of particular interest to the deep-time paleocommunity because prior to the evolution of foraminifera, and because deep sea sediments older than 180 million years are rare, many calcareous fossils available for δ11B analysis thrived in shallow marine habitats. As efforts continue to find deep-time analogs to modern ocean acidification, low-pH groundwater discharge in coastal zones may complicate interpretations of δ11B results but may be addressed by a rigorous multi-proxy approach.This dissertation provides a record of coastal and climate change during recent periods of climate variability and sea-level rise over the last 5,000 years to provide context for current climate change in the tropics and an understanding of drivers of variability in the past and the future at low latitude sites.

The creeks of the San Mateo Point watershed empty into the Pacific Ocean at the intersection of San Onofre State Beach, Marine Corps Base Camp Pendleton, and a famous group of surf breaks called Trestles in Southern California. This site brings into view several transecting borders: land/water, public/private, human/non-human and recreational/militaristic/environmental. This dissertation explores the disjunctive intersection of these borders in the production of what I term “Trestles’ surfscape.” The term reworks Appadurai's “globalscapes” with Lefebvre’s “production of space,” and the more recent calls for an “amphibious anthropology” by René ten Bos. This dissertation is an ethnography of “Save Trestles,” a campaign to save San Onofre State Beach and its world-famous surf breaks from the development of an eight-lane, sixteen-mile toll road extension. The campaign demonstrates sophisticated social-change networking and advocacy that considers the coupling of human-natural systems. Social actors include the Juaneño Band of Mission Indians, Acjachemen Nation, scientists, surfers, the global surfing industry and transportation agencies. In 2016, a legal settlement prohibited any future transportation projects through the state beach/park; stakeholders celebrated, declaring Trestles “saved forever.” I employ a transdisciplinary methodology to show how the political ecology of Trestles’ surfscape reveals an elaborate web of relationships between (non)humans and their lived environments, past and present, local and global. My methodology is rooted in the ocean literacy I acquired as a surfer, as well as data-gathering techniques I learned as a citizen scientist for the Urban Tides initiative. This dissertation calls into question the success of the campaign given that rising sea levels remain Trestles’ ultimate threat. Furthermore, the push to build a toll road near San Clemente continues, and climate change science is under assault. This case study is organized into four chapters. The first chapter provides a historical overview of the production of Trestles’ surfscape. The second chapter focuses on the campaign to “Save Trestles.” Chapter 3 looks at the contemporary surfscape as an abject anthropogenic space. The last chapter turns to the Urban Tides Initiative and concerns over the impact that sea-level rise will have on Trestles’ economic future.

Sea-level rise (SLR) threatens coastal communities by increasing flood exposure for people, homes, businesses, and critical infrastructure. In order to protect residents and the infrastructure systems on which they rely, coastal communities will need to plan for and adapt to higher sea levels and increased flood hazards. This dissertation contributes to the understanding of SLR impacts on human, engineered, and natural systems. More specifically, the text addresses three important aspects of SLR adaptation: the need for data-driven methods to inform regional SLR adaptation networks, the impacts of SLR on critical infrastructure and service disruptions, and the influence of coupled SLR, precipitation, and storm surge on coastal groundwater aquifers and flooding.Many collaborative networks aimed at promoting SLR adaptation at the global, national, or regional scale are primarily based on geographic proximity or voluntary participation and are not grounded in any quantitative assessment of shared vulnerability. The first part of this dissertation presents a method to group communities based on similar SLR exposure variables using statistical cluster analysis. The method is applied to cities and counties in the San Francisco Bay Area to demonstrate the usefulness for developing regional SLR adaptation networks.In coastal communities, critical infrastructure assets, such as wastewater treatment plants, are susceptible to flooding due to SLR. However, the extent and progression of this exposure and the impacts on service disruptions are poorly understood. The second part of this work presents a geospatial analysis of wastewater exposure to SLR-induced marine flooding at the national scale and a similar analysis of SLR-induced groundwater flooding at the regional scale in the San Francisco Bay Area. Overall, hundreds of wastewater treatment plants could face flood disruptions due to SLR, which could lead to a loss of wastewater services for millions of residents. In some cases, groundwater is more of a threat than marine flooding.To understand the potential impacts of SLR on coastal groundwater aquifers and flooding, most previous studies have used steady-state methods and have focused on SLR and other climate factors, such as precipitation, separately. However, the strong coupling between precipitation and other weather variables that influence coastal water levels suggests a need for multivariate approaches. The final part of this dissertation describes the use of a copula approach to correlate precipitation with wind speed and atmospheric pressure. These variables are then used to determine changes in water levels due to wind setup and pressure-driven surge under current and future climate scenarios. Forcing a groundwater model with this data provides insight into the potential for a narrower unsaturated zone and groundwater emergence.Together, these chapters explore the local disruptions and regional impacts of SLR, as well as the coupled processes that lead to flooding.

Predicted sea-level rise (SLR) could have catastrophic impacts on the coastal zone. Salt marshes have evolved under low SLR, but their resilience to higher rates is uncertain. Assessing vulnerabilities of California’s salt marshes is a case study of the diversity and scale of problems that land managers will face. The major questions of this study were: 1) Are recent sediment budgets allowing southern California salt marshes to keep pace with SLR; 2) within its current range, how vulnerable are two sub-species of Ridgway’s rail (Rallus obsoletus; rails), a low elevation salt marsh specialist, to SLR; and 3) within its current range, how vulnerable are Belding’s savannah sparrows (Passerculus sandwichensis beldingi; sparrows), a high elevation salt marsh specialist, to SLR? To answer the first question, tidal creek sediment fluxes were measured in two sites with different levels of adjacent urbanization. To answer the second and third questions, original and pre-existing wildlife and habitat data were compiled at 17 sites to forecast habitat suitability. Storms and high tides led to sediment import in tidal creeks at Mugu and Seal. While sediment budgets were balanced during the dry study period, Seal’s elevation declined, and Mugu’s elevation plateaued, suggesting that only Mugu would persist if SLR rate stabilizes. For the Ridgway’s Rail study, under a SLR scenario of +166cm/100yr, suitable habitat for the San Francisco Bay Area’s (SF) sub-species will increase by 35% at mid-century, and current breeding habitat extent for Southern California’s (SC) sub-species will increase by 24%. However, by 2100, SF will lose 84% of suitable habitat and SC will lose 80% of its current habitat extent. Furthermore, six salt marshes will lose over 95% of suitable habitat. Under the same scenario, the current extent of Belding’s Savannah sparrow habitat will contract by 61% at mid-century before completely drowning by 2100. Results from the habitat suitability studies indicate that if no major adaptations, such as protecting the shoreline, increasing elevations, restoring marsh drainage, facilitating marsh migration, and restoring sediment delivery, are implemented soon, salt marsh-dependent wildlife in the majority of California coastal zones will be extirpated by 2100 under high SLR scenarios.

Waves overtop berms and seawalls along the shoreline of Imperial Beach (IB), CA when energetic winter swell and high tide coincide. These intermittent, few-hour long events flood low-lying areas and pose a growing inundation risk as sea levels rise. To support city flood response and management, an IB flood warning system was developed. Total water level (TWL) forecasts combine predictions of tides and sea-level anomalies with wave runup estimates based on incident wave forecasts and the nonlinear wave model SWASH. In contrast to widely used empirical runup formulas that rely on significant wave height and peak period, and use only a foreshore slope for bathymetry, the SWASH model incorporates spectral incident wave forcing and uses the cross-shore depth profile. TWL forecasts using a SWASH emulator demonstrate skill several days in advance. Observations set TWL thresholds for minor and moderate flooding. The specific wave and water level conditions that lead to flooding, and key contributors to TWL uncertainty, are identified. TWL forecast skill is reduced by errors in the incident wave forecast and the one-dimensional runup model, and lack of information of variable beach morphology (e.g., protective sand berms can erode during storms). Model errors are largest for the most extreme events. Without mitigation, projected sea-level rise will substantially increase the duration and severity of street flooding. Application of the warning system approach to other locations requires incident wave hindcasts and forecasts, numerical simulation of the runup associated with local storms and beach morphology, and model calibration with flood observations.

Wide estuaries are natural magnets for urban development. Several of the World’s major cities developed around estuaries, but at the same time encroached upon some of the most complex and vital ecosystems. Sea-level rise threatens to submerge both rare wetland habitat and essential urban areas and infrastructure. This prospect discloses the urgency of balancing urban development and environmental protection in Metropolitan Estuaries. The hard task of dealing with this threat may provide the opportunity to promote an integrated approach to regional planning, where the necessary adaptation of cities to sea-level rise could equally promote the preservation, or even the enhancement, of wetland habitat.The two case study metropolitan estuaries, San Francisco Bay (California, USA) and the Tagus Estuary (Lisbon, Portugal), share striking similarities in terms of morphology. They both host large metropolitan areas and important wetland ecosystems. Nevertheless, a finer analysis of development patterns reveals crucial differences in the extent of shoreline alteration and types of land use that now encroach upon natural estuarine habitat. The comparative study of both estuaries provides mutually beneficial insights on the shortcomings of each system, and helps identify opportunities to enhance coastal zone management, adaptive governance and environmental planning efforts.The evolution of both estuaries throughout the Holocene is reconstructed, with special emphasis on the process of anthropogenic alteration. While this impact has been significant and continuous in the Tagus Estuary for over two millennia, large scale disturbance of the San Francisco Bay was concentrated in the last two centuries. The legal frameworks that have guided, with varying degrees of effectiveness, the process of wetland reclamation and landfilling share a common ancestry in the Roman Law. These have evolved continuously in Lisbon and the State has upheld with relative success the provision to keep estuarine lowlands in public control, even as they were steadily transformed to farmland. In San Francisco, a period of deep disturbances over the Sacramento River’s hydrology was coupled with extremely fast and under regulated development of lowlands. During a short period, the property of these lands, which would theoretically fall within the Public Trust, was transferred to local governments and private landowners, which led to their steady transformation onto salt ponds, industrial zones and even residential neighborhoods. As a consequence, the Bay Area now has extensive developed areas at very low elevations, vulnerable to low levels of sea-level rise, and remaining wetlands are now heavily encroached upon by urban development. Around the Tagus Estuary, while most original wetlands have long been drained for farmland, the remaining patches are adjacent to non-urban land uses, which could facilitate future efforts of restoration or allow wetland migration with rising seas.A comparative modelling of sea-level rise flooding over existing land uses reveals that, while around the Tagus Estuary most reclaimed lowlands are reserved for farmland and urban development over landfill is limited, the extent of developed urban areas at very low elevations is much greater around the SF Bay, which renders the region more vulnerable to early stages of SLR. Nonetheless, both cities have begun to incorporate climate adaptation onto their main environmental planning blueprints, for which they can be seen as early adopters of local sea-level rise adaptation strategies. Through interviews with stakeholders and document analysis, the planning and decision-making exercises that led to the recent elaboration of the first Tagus Estuary Management Plan, and the Bay Plan Climate Change Amendment, are analyzed and discussed.Lisbon benefits from a very simple, top-down, planning structure, with a handful of public entities directly communicating and articulating stakes and approaches along the planning process. A lack of transparency as to some specific interventions and a still somewhat incipient tradition of public participation have contributed to protract the Plan’s final approval.The Bay Area institutional framework is well-used to collaborative planning efforts, which are usually successful in articulating conflicting interests, but are prone to limitations derived from narrow, and often difficult to expand, mandates for environmental planning agencies, within an extremely complex, multi-level, governance structure involving three levels of government and very active interest groups. While broad mitigation/adaptation strategies are decided at the National or State levels, the actual implementation of SLR adaptation measures often require a great deal of involvement of local actors. Given that it is at this juncture that adaptation takes a concrete spatial expression, this is also the moment when land-use conflicts arise. Local governments are left with much of the burden of mediating competing interests, between urban development, environmental protection, and other social demands. In some instances, the prospect of shoreline development may be very attractive for both property owners/developers and local governments, given the potential land value and economic benefits, but these have to be weighed against the medium-/long-term costs of defending these assets from rising sea-levels.In San Francisco Bay, there is an increasing awareness of the challenges posed by SLR, but the institutional arrangements are complex, and communication between the different public agencies/departments is not always as streamlined as it could be. Some agencies and departments need to adapt their procedures in order to remove institutional barriers to adaptation, but path dependence is an obstacle. The several projects where different federal and state agencies are partnered with local governments highlight the benefits of a more frank and regular communication between public actors. It also emphasizes the benefits of a coordination of efforts and strategies, something that was eroded in the transition from government-led policies to a new paradigm of local-based adaptive governance.Whereas the articulation of public actors is often easy to address by increasing communication and coordination, conflicts involving private landowners and developers may be much complicated by the threat of litigation. The lack of a strong legal backing to public environmental protection mandates is a major obstacle to shoreline planning around the Bay and elsewhere, and this is highlighted by the extreme caution of some public agencies in upholding their jurisdictions over private property. Environmental NGOs have, in the case of California, a big role to play, as they are able to resort to the same legal and lobbying instruments as the developers, and may help even-out the field between public stakeholders with limited legal and economic resources, and powerful private developers with nothing to lose. There is seemingly a sense of urgency in pushing for the development of shoreline properties, as public opposition to development on locations exposed to SLR is most likely to increase in the coming decades. At the same time, NGOs and public agencies are aware of the stress wetlands will be under as the rates of SLR increase towards the end of the century.“Green”, or ecosystem-based, adaptation is already on the way around the Bay. Large scale wetland restoration projects have already been concluded, and further action now often requires articulation with the reinforcement of flood defense structures, given the level of urban encroachment. While levee setback, or removal, would provide greater environmental benefit, the need to protect urban areas and infrastructure has led to the trial of ingenious solutions for promoting wetland resilience while upgrading the level of protection granted by levees.

Using ArcGIS, a sea-level rise inundation comparison was conducted using four different techniques under five sea-level rise conditions for the Kauai, Hawaii, towns of Hanalei Bay, Kapa'a, and Waimea. Sea-level rise was mapped in 0.5 m increments from 0.0 m of rise to 2.0 m of rise. Datasets used in the analysis include a digital elevation model (DEM) layer, wave height data, tidal elevation data, and land cover data. The four techniques illustrating projected inundation serve as a comparison of passive versus dynamic models. The primary goals of this study were to not only compare passive and dynamic sea-level rise inundation models, but also to provide a realistic representation of what future sea-level rise will look like on Kauai, and which areas would be inundated at specific future water surface levels. The results of this analysis can be used to aid Kauai government officials in planning for the future and to aid in prioritizing where and what infrastructure and development will need to be considered before actual sea-level rise impacts occur.

Tidal wetland ecosystems are dynamic coastal habitats that, in California, often occur at the complex nexus of aquatic environments, diked and leveed baylands, and modified upland habitat. Because of their prime coastal location and rich peat soil, many wetlands have been reduced, degraded, and/or destroyed, and yet their important role in carbon sequestration, nutrient and sediment filtering, flood control, and as habitat requires us to further research, conserve, and examine their sustainability, particularly in light of predicted climate change. Predictions of regional climate change effects for the San Francisco Bay Estuary present a future with reduced summer freshwater input and increased sea levels, resulting in higher estuarine salinities throughout the growing season, increased saline influence in brackish and freshwater marshes, and increased depth and duration of inundation. Experimentally testing, monitoring across scales, and spatially modeling the responses of dominant wetland vegetation to the substantial predicted climate change effects are among the critical threads of knowledge needed to understand how this estuary and others along the Pacific coast might respond to significant changes in physical drivers and community interactions. My dissertation research focused on possibilities for wetland resilience in a changing climate in the San Francisco Bay Estuary across scales and using a suite of methodologies.Tidal wetland resilience to predicted sea-level rise requires an understanding of both individual plant and community-level responses in addition their interactions with sediment supply and adjacent land uses. Through a large field experiment simulating sea-level rise, I found that wetland plants have a high tolerance for increases in inundation in the short term and that community interactions need to be incorporated into plant responses to increased sea-level rise. Scaling measurements of plant production up to the site level and across landscapes requires the integration of field measurements with remotely sensed measurements. Investigating remote sensing techniques of measuring carbon stock, I found that the presence of dense standing plant litter common in Pacific coast freshwater wetlands can hinder the ability to find a reliable way of measuring plant production remotely. Finally, I was able to successfully calibrate an ecogeomorphic mechanistic model for wetland accretion across four wetlands in the San Francisco Bay Estuary and examine potential wetland resiliency under a range of sea-level rise scenarios. At sea-level rise rates 100 cm/century and lower, wetlands remained vegetated. Once sea levels rise above 100 cm, marshes begin to lose ability to maintain elevation, and the presence of adjacent upland habitat becomes increasingly important for marsh migration. Results from this study emphasize that the wetland landscape in the bay is threatened with rising sea levels, and there are a limited number of wetlands that will be able to migrate to higher ground as sea levels rise. Despite these challenges, my dissertation presents a robust and new understanding of how tidal wetlands might respond to predicted climate change.

California's sandy shorelines are important resources in terms of ecological habitat, recreation and tourism, and aesthetic beauty. They also serve as important natural buffers, often protecting back-beach development and infrastructure from wave attack. Encroachment or fixing of the back beach in conjunction with sea-level rise will reduce the accommodation space of beaches and subsequently increase the vulnerability of the back beach to extreme water level events associated with storms. Understanding the present state of California's sandy shorelines in terms of landward migration potential, vulnerability to extreme water events, and local morphodynamic variability is important for coastal policymakers and managers to make informed decisions regarding the future of the California coastline. In this study, the landward migration potential of California's beaches was assessed through a statewide cataloging and classification of all sandy shorelines in the context of back beach immobility and restrictions to landward migration. Beach inundation vulnerability from increased frequency of high water events with rising sea level was determined with extreme water level exceedance distributions from historic tide gauge records and sea-level rise projections of 18 cm, 79 cm, and 140 cm by 2100. Finally, alongshore variability and the influence of high wave events and berm overtopping on beach profile morphodynamics were analyzed through seasonal beach surveying of a coastal lagoon pocket beach. Fifty-eight percent of the total length of sandy shoreline in California is restricted in the back beach from landward migration. This is primarily due (in Central and Southern California) to anthropogenic coastal development and infrastructure. Beach inundation potential from extreme high water events is highly variable and is a function of berm height and backshore morphology. Backshore morphology influences foreshore and berm morphodynamics by modifying swash sediment transport. The growth and persistence of a berm on a bar-built coastal lagoon beach is dependent on berm overtopping; however, overtopping beyond a threshold frequency becomes destructive and can lead to berm erosion. While statewide more than half of California's sandy shorelines are being threatened by reduced accommodation space through terrestrial and marine encroachment, understanding local variability is essential for determining the future of these highly valued resources.

Sea-level rise is a problem that affects regions worldwide - from the marshlands of the San Francisco Bay Area to the farmlands in coastal Bangladesh. Three-dimensional ice sheet models are the principle tools to evaluate mass loss from ice sheets that contribute to sea-level rise. We recognize that given the current limitations in representing the full extent of dynamical processes that affect ice sheet mass loss in 3-D ice sheet models, we cannot make reliable forecasts of sea-level rise from melting polar land ice. Thus, we take a completely different approach to gaining insight about the potential effects of climate change-induced perturbations on ice sheets. We build a flowline model that resolves the fast-flowing portions of ice sheets (i.e., ice streams). We express the dynamics along the flowline with (a) vertical shear deformation, (b) horizontal shear deformation, and (c) basal slip. Knowledge accumulated from prior force balance analyses performed on some polar ice streams allows us to form relations between (a) and (c), and between (a) and (c) combined and (b). Based on these relationships, we numerically construct surface elevation profiles along flowlines centered on ten select ice streams in Greenland and Antarctica, by prescribing three climate change-induced perturbations: grounding line retreat, ice stream widening, and surface mass balance increase. Comparing these constructed profiles to the current observed ones allows us to quantify the effect of these perturbations on the various characteristics that these ten ice streams possess. Pine Island Glacier, which flows over a long overdeepening, will lose more than half of its stored ice volume that is contributable to sea-level rise before it reaches a possible steady state. Recovery Ice Stream, with its slippery base, long stretch of streaming-flow, and longest flowline among those we examined, loses the most mass (812 km3/km width). Jutulstraumen, which has little room to widen and a short stretch of streaming-flow, experiences more mass gain due to surface mass balance increase than mass loss due to grounding line retreat and widening. The broad range of ice streams and their diverse responses to prescribed perturbations is a convincing message that an accurate assessment of the contribution of ice sheets to future sea-level rise can only be obtained by raising the resolution of models to resolve the fast-flowing features and looking at their mass changes individually over time.

Two populations of a declining western North American freshwater turtle—one coastal and one inland—were exposed to elevated water salinities of 10 ppt and 15 ppt over 2 weeks. Turtles from the coastal estuarine population had reduced feeding and drinking and maintained lower plasma osmolality levels than did those from inland., Sea-level rise, drought and water diversion can all lead to rapid salinization of freshwater habitats, especially in coastal areas. Increased water salinities can in turn alter the geographic distribution and ecology of freshwater species including turtles. The physiological consequences of salinization for freshwater turtles, however, are poorly known. Here, we compared the osmoregulatory response of two geographically separate populations of the freshwater Western Pond Turtle (Actinemys marmorata)—a species declining across its range in western North America—to three constant salinities: 0.4 ppt, 10 ppt and 15 ppt over 2 weeks. We found that turtles from a coastal estuarine marsh population regulated their plasma osmolality at lower levels than their conspecifics from an inland freshwater creek population 45 km away. Plasma osmolalities were consistently lower in estuarine marsh turtles than the freshwater creek turtles over the entire 2-week exposure to 10 ppt and 15 ppt water. Furthermore, estuarine marsh turtles maintained plasma osmolalities within 1 SD of their mean field osmolalities over the 2-week exposure, whereas freshwater creek turtles exceeded their field values within the first few days after exposure to elevated salinities. However, individuals from both populations exhibited body mass loss in 15 ppt water, with significantly greater loss in estuarine turtles. We speculate that the greater ability to osmoregulate by the estuarine marsh turtles may be explained by their reduced feeding and drinking in elevated salinities that was not exhibited by the freshwater creek population. However, due to mass loss in both populations, physiological and behavioural responses exhibited by estuarine marsh turtles may only be effective adaptations for short-term exposures to elevated salinities, such as those from tides and when traversing saline habitats, and are unlikely to be effective for long-term exposure to elevated salinity as is expected under sea-level rise.

Fossil-fuel resources are sufficient to eliminate the Antarctic Ice Sheet., The Antarctic Ice Sheet stores water equivalent to 58 m in global sea-level rise. We show in simulations using the Parallel Ice Sheet Model that burning the currently attainable fossil fuel resources is sufficient to eliminate the ice sheet. With cumulative fossil fuel emissions of 10,000 gigatonnes of carbon (GtC), Antarctica is projected to become almost ice-free with an average contribution to sea-level rise exceeding 3 m per century during the first millennium. Consistent with recent observations and simulations, the West Antarctic Ice Sheet becomes unstable with 600 to 800 GtC of additional carbon emissions. Beyond this additional carbon release, the destabilization of ice basins in both West and East Antarctica results in a threshold increase in global sea level. Unabated carbon emissions thus threaten the Antarctic Ice Sheet in its entirety with associated sea-level rise that far exceeds that of all other possible sources.

doi: http://dx.doi.org/10.15447/sfews.2015v13iss1art3In this paper, we report on the adaptation and application of a one-dimensional marsh surface elevation model, the Wetland Accretion Rate Model of Ecosystem Resilience (WARMER), to explore the conditions that lead to sustainable tidal freshwater marshes in the Sacramento–San Joaquin Delta. We defined marsh accretion parameters to encapsulate the range of observed values over historic and modern time-scales based on measurements from four marshes in high and low energy fluvial environments as well as possible future trends in sediment supply and mean sea level. A sensitivity analysis of 450 simulations was conducted encompassing a range of porosity values, initial elevations, organic and inorganic matter accumulation rates, and sea-level rise rates. For the range of inputs considered, the magnitude of SLR over the next century was the primary driver of marsh surface elevation change. Sediment supply was the secondary control. More than 84% of the scenarios resulted in sustainable marshes with 88 cm of SLR by 2100, but only 32% and 11% of the scenarios resulted in surviving marshes when SLR was increased to 133 cm and 179 cm, respectively. Marshes situated in high-energy zones were marginally more resilient than those in low-energy zones because of their higher inorganic sediment supply. Overall, the results from this modeling exercise suggest that marshes at the upstream reaches of the Delta—where SLR may be attenuated—and high energy marshes along major channels with high inorganic sediment accumulation rates will be more resilient to global SLR in excess of 88 cm over the next century than their downstream and low-energy counterparts. However, considerable uncertainties exist in the projected rates of sea-level rise and sediment avail-ability. In addition, more research is needed to constrain future rates of aboveground and belowground plant productivity under increased CO2 concentrations and flooding.