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At least 289 records · Page 16Linked to original sources

USGS2003

The sedimentary record of climatic and anthropogenic influence on the Patuxent estuary and Chesapeake Bay ecosystems

Ecological and paleoecological studies from the Patuxent River mouth reveal dynamic variations in benthic ostracode assemblages over the past 600 years due to climatic and anthropogenic factors. Prior to the late 20th century, centennial-scale changes in species dominance were influenced by climatic and hydrological factors that primarily affected salinity and at times led to oxygen depletion. Decadal-scale droughts also occurred resulting in higher salinities and migration of ostracode species from the deep channel (Loxoconcha sp., Cytheromorpha newportensis) into shallower water along the flanks of the bay. During the 19th century the abundance of Leptocythere nikraveshae and Perissocytheridea brachyforma suggest increased turbidity and decreased salinity. Unprecedented changes in benthic ostracodes at the Patuxent mouth and in the deep channel of the bay occurred after the 1960s when Cytheromorpha curta became the dominant species, reflecting seasonal anoxia. The change in benthic assemblages coincided with the appearance of deformities in foraminifers. A combination of increased nitrate loading due to greater fertilizer use and increased freshwater flow explains this shift. A review of the geochemical and paleoecological evidence for dissolved oxygen indicates that seasonal oxygen depletion in the main channel of Chesapeake Bay varies over centennial and decadal timescales. Prior to 1700 AD, a relatively wet climate and high freshwater runoff led to oxygen depletion but rarely anoxia. Between 1700 and 1900, progressive eutrophication occurred related to land dearance and increased sedimentation, but this was superimposed on the oscillatory pattern of oxygen depletion most likely driven by climatological and hydrological factors. It also seems probable that the four- to five-fold increase in sedimentation due to agricultural and timber activity could have contributed to an increased natural nutrient load, likely fueling the early periods (1700-1900) of hypoxla prior to widespread fertilizer use. Twentieth-century anoxia worsened in the late 1930s-1940s and again around 1970, reaching unprecedented levels in the past few decades. Decadal and interannual variability in oxygen depletion even in the 20th century is still strongly influenced by climatic processes influencing precipitation and freshwater runoff.

Estuaries↗

USGS2018

100-year lower Mississippi floods in a global climate model: Characteristics and future changes

Floods in the Mississippi basin can have large negative societal, natural, and economic impacts. Understanding the drivers of floods, now and in the future, is relevant for risk management and infrastructure-planning purposes. We investigate the drivers of 100-yr-return lower Mississippi River floods using a global coupled climate model with an integrated surface water module. The model provides 3400 years of physically consistent data from a static climate, in contrast to available observational data (relatively short records, incomplete land surface data, transient climate). In the months preceding the model’s 100-yr floods, as indicated by extreme monthly discharge, above-average rain and snowfall lead to moist subsurface conditions and the buildup of snowpack, making the river system prone to these major flooding events. The meltwater from snowpack in the northern Missouri and upper Mississippi catchments primes the river system, sensitizing it to subsequent above-average precipitation in the Ohio and Tennessee catchments. An ensemble of transient forcing experiments is used to investigate the impacts of past and projected anthropogenic climate change on extreme floods. There is no statistically significant projected trend in the occurrence of 100-yr floods in the model ensemble, despite significant increases in extreme precipitation, significant decreases in extreme snowmelt, and significant decreases in less extreme floods. The results emphasize the importance of considering the fully coupled land–atmosphere system for extreme floods. This initial analysis provides avenues for further investigation, including comparison to characteristics of less extreme floods, the sensitivity to model configuration, the role of human water management, and implications for future flood-risk management.

Journal of Hydrometeorology↗

USGS2016

Hydrologic response of desert wetlands to Holocene climate change: preliminary results from the Soda Springs area, Mojave National Preserve, California

Desert wetlands are common features in arid environments and include a variety of hydrologic facies, including seeps, springs, marshes, wet meadows, ponds, and spring pools. Wet ground conditions and dense stands of vegetation in these settings combine to trap eolian, alluvial, and fluvial sediments that accumulate over time. The resulting deposits are collectively called ground-water discharge (GWD) deposits, and contain information on how small desert watersheds responded to climate change in the past. Most GWD studies in the southwestern U.S. have focused on the late Pleistocene because the Holocene was too dry to support the extensive wetland systems that were so pervasive just a few millennia earlier. Here we describe the results of a pilot project that involves coring extant wetlands and analyzing the sedimentology and microfauna of the recovered sediment to infer Holocene hydrologic conditions. In 2011, a series of cores were taken near wetlands situated along the western margin of the Soda Lake basin in the Mojave National Preserve of southern California. The core sediments appear to show that the wetlands responded to the relatively minor climate fluctuations that characterized the Holocene. However, our analysis was limited by relatively low sediment recovery (which only averaged 70-80%) and a general paucity of datable materials in the cores. Additional studies aimed at improving recovery and developing new techniques for concentrating plant microfossils (plant remains that are <150 m in diameter) for radiocarbon dating are ongoing.

Conference Paper↗

USGS2023

U.S. Geological Survey science vision for native freshwater mussel research in the United States

Executive Summary North America is a global center for native freshwater mussel (order Unionida, hereinafter “mussels”) diversity, with more than 350 species. Mussels are among the most imperiled fauna on the planet. Reasons for both local and widespread declines in mussels are mostly unknown, although the threats may include habitat loss and fragmentation, diseases, environmental contaminants, altered flow regimes, migration barriers to larval hosts, non-native species, and climate change. Over the past three decades, research on mussels has been substantial. Nevertheless, current conservation and management efforts are limited by significant information gaps. For example, the effects of emerging stressors on mussels are largely unknown and identifying when habitats are rehabilitated and suitable for reestablishment of mussels remains challenging. Additionally, historical and current information on the distribution, taxonomy, and life histories are often unreliable or lacking altogether, and more reliable information is needed for many species. We identified focal research themes, goals, and objectives where research on mussels is needed based on information gaps identified through conversations with resource partners across local, regional, and national organizations. Research on biodiversity seeks to enhance the diversity of mussel species and populations to support healthy aquatic ecosystems. Research on emerging stressors seeks to improve the understanding of how mussel species, populations, and communities respond to emerging stressors, including environmental contaminants and climate change. Research on conservation seeks to enhance the recovery of species and populations and to identify data gaps limiting the conservation of mussels and their habitats. Mussels are in urgent need of proactive conservation because they are an integral part of our natural heritage, enhance biodiversity, and provide vital ecological services that support freshwater ecosystems. The U.S. Geological Survey (USGS) has been, and continues to be, a leader in mussel research. Although the USGS is well suited to address the broad-scale multidisciplinary research needed to conserve mussels, the USGS has had substantial loss of scientists with mussel expertise over the past 20 years. However, the breadth of the USGS expertise on mussels can be leveraged internally across other USGS mission and program areas and externally across research partners. Given the breadth and scope of the issues facing mussels across the United States, the research themes outlined in this science vision can only be accomplished through extensive collaborations between the USGS and the full spectrum of natural resource partners, including other Federal and State agencies, Tribal organizations, universities, industries, and nongovernmental organizations.

Circular↗

USGS2011

Late Pliocene and Quaternary Eurasian locust infestations in the Canary Archipelago

The Canary Archipelago has long been a sensitive location to record climate changes of the past. Interbedded with its basalt lavas are marine deposits from the principal Pleistocene interglacials, as well as aeolian sands with intercalated palaeosols. The palaeosols contain African dust and innumerable relict egg pods of a temperate‐region locust (cf. Dociostaurus maroccanus Thunberg 1815 ). New ecological and stratigraphical information reveals the geological history of locust plagues (or infestations) and their palaeoclimatic significance. Here, we show that the first arrival of the plagues to the Canary Islands from Africa took place near the end of the Pliocene, ca. 3 Ma, and reappeared with immense strength during the middle Late Pleistocene preceding MIS (marine isotope stage) 11 (ca. 420 ka), MIS 5.5 (ca. 125 ka) and probably during other warm interglacials of the late Middle Pleistocene and the Late Pleistocene. During the Early Holocene, locust plagues may have coincided with a brief cool period in the current interglacial. Climatically, locust plagues on the Canaries are a link in the chain of full‐glacial arid–cold climate (calcareous dunes), early interglacial arid–sub‐humid climate (African dust inputs and locust plagues), peak interglacial warm–humid climate (marine deposits with Senegalese fauna), transitional arid–temperate climate (pedogenic calcretes), and again full‐glacial arid–cold climate (calcareous dunes) oscillations. During the principal interglacials of the Pleistocene, the Canary Islands recorded the migrations of warm Senegalese marine faunas to the north, crossing latitudes in the Euro‐African Atlantic. However, this northward marine faunal migration was preceded in the terrestrial realm by interglacial infestations of locusts.

Lethaia↗

USGS2022

Voluntary Guidance for States to Incorporate Climate Adaptation in State Wildlife Action Plans and Other Management Plans

The Voluntary Guidance for States to Incorporate Climate Adaptation into State Wildlife Actions Plans and other Management Plans aims to help state fish and wildlife agencies incorporate climate change adaptation for fish and wildlife and their habitats into State Wildlife Action Plans (SWAPs) and other natural resource management plans. This update to the original 2009 Voluntary Guidance reflects the advancements in climate science and in our understanding and implementation of climate adaptation developed over the past 13 years. The document provides principles and tools that can be used to plan for and implement climate change adaptation, voluntary guidance for incorporating climate change into the existing required elements of SWAPs, and case studies to demonstrate adaptation strategies deployed by states in their management efforts. Climate change continues to be a significant issue for wildlife and natural systems and for the people who rely on the ecosystem services they provide. There is now a well-established and growing scientific literature on the impacts of climate change on wildlife and their habitats, including climate-driven range shifts, population changes, and even species extinctions. At the same time, efforts to address climate change impacts can be made in cooperation with efforts to address other threats, including habitat loss/fragmentation from development, introduction of invasive species, water pollution, and wildlife diseases, many of which may be exacerbated by climate change. Since climate change is a complex and often politically charged issue, it is understood that the decision to revise SWAPs, or other plans, to address climate change rests solely with each state fish and wildlife agency. All states are required to update their SWAPs by 2025 to qualify for federal funding. Although consideration of climate change is not a requirement for this revision of SWAPs, assessing the impacts of climate change and identifying species and habitats vulnerable to those impacts can help states meet the required eight elements for the revision and prepare for funding opportunities that can support climate adaptation efforts. The Inflation Reduction Act of 2022 and the Recovering America’s Wildlife Act, if passed by the Senate, would provide billions of dollars to states to implement SWAPs, including addressing climate change impacts on fish and wildlife. The Voluntary Guidance Document introduces and explains seven overarching principles for incorporating climate adaptation into SWAPs. These principles (found in Chapter 2) are: 1. Fully integrate climate change into SWAPs 2. Adopt forward-looking goals 3. Explicitly link actions to climate vulnerabilities 4. Manage for change, not just persistence 5. Consider broader landscapes and longer timeframes 6. Address uncertainty by considering future scenarios and use of adaptive management 7. Engage diverse partners with climate experience and expertise

Report↗

USGS2009

Chemical weathering of a marine terrace chronosequence, Santa Cruz, California. Part II: Solute profiles, gradients and the comparisons of contemporary and long-term weathering rates

The spatial and temporal changes in hydrology and pore water elemental and 87 Sr/ 86 Sr compositions are used to determine contemporary weathering rates in a 65- to 226-kyr-old soil chronosequence formed from granitic sediments deposited on marine terraces along coastal California. Soil moisture, tension and saturation exhibit large seasonal variations in shallow soils in response to a Mediterranean climate. These climate effects are dampened in underlying argillic horizons that progressively developed in older soils, and reached steady-state conditions in unsaturated horizons extending to depths in excess of 15 m. Hydraulic fluxes (q h ), based on Cl mass balances, vary from 0.06 to 0.22 m yr -1 , resulting in fluid residence times in the terraces of 10-24 yrs. As expected for a coastal environment, the order of cation abundances in soil pore waters is comparable to sea water, i.e., Na > Mg > Ca > K > Sr, while the anion sequence Cl > NO 3 > HCO 3 > SO 4 reflects modifying effects of nutrient cycling in the grassland vegetation. Net Cl-corrected solute Na, K and Si increase with depth, denoting inputs from feldspar weathering. Solute 87 Sr/ 86 Sr ratios exhibit progressive mixing of sea water-dominated precipitation with inputs from less radiogenic plagioclase. While net Sr and Ca concentrations are anomalously high in shallow soils due to biological cycling, they decline with depth to low and/or negative net concentrations. Ca/Mg, Sr/Mg and 87 Sr/ 86 Sr solute and exchange ratios are similar in all the terraces, denoting active exchange equilibration with selectivities close to unity for both detrital smectite and secondary kaolinite. Large differences in the magnitudes of the pore waters and exchange reservoirs result in short-term buffering of the solute Ca, Sr, and Mg. Such buffering over geologic time scales can not be sustained due to declining inputs from residual plagioclase and smectite, implying periodic resetting of the exchange reservoir such as by past vegetational changes and/or climate. Pore waters approach thermodynamic saturation with respect to albite at depth in the younger terraces, indicating that weathering rates ultimately become transport-limited and dependent on hydrologic flux. Contemporary rates R solute are estimated from linear Na and Si pore weathering gradients b solute such that R solute = frac(q h , b solute ?? S v ) where S v is the volumetric surface area and ?? is the stoichiometric coefficient. Plagioclase weathering rates (0.38-2.8 ?? 10 -15 mol m -2 s -1 ) are comparable to those based on 87 Sr/ 86 Sr mass balances and solid-state Na and Ca gradients using analogous gradient approximations. In addition, contemporary solute gradients, under transport-limited conditions, approximate long-term solid-state gradients when normalized against the mass of protolith plagioclase and its corresponding aqueous solubility. The multi-faceted weathering analysis presented in this paper is perhaps the most comprehensive yet applied to a single field study. Within uncertainties of the methods used, present day weathering rates, based on solute characterizations, are comparable to average long-term past rates as evidenced by soil profiles.

Geochimica et Cosmochimica Acta↗

USGS2023

Blue carbon in a changing climate and a changing context

Blue carbon, a convenient term to encompass the climate mitigation value of coastal carbon dynamics, has received global policy attention and growing datasets to support management actions. Carbon stock assessments in mangroves, seagrass, and tidal marshes document significant carbon storage in soils. Models illustrate significant downward fluxes of carbon dioxide and limited methane emissions, making tidal wetland preservation and restoration notably potent for carbon dioxide removal (CDR). Natural variation in different carbon stocks and fluxes has led to prioritization efforts to characterize coastal lands across physical and biological gradients. However, a larger concern beyond upscaling carbon dynamics is the resilience of these stocks and fluxes with global changes. Data-informed models have greatly improved our assessments of the vulnerability of soil and biomass stocks, greenhouse gas (GHG) balance, and spatial extents. Accelerated sea-level rise is increasingly concerning, but its impacts vary by resilience context, as very few coastal lands are without direct human impact. As the landscape context has changed, blue carbon fluxes have also shifted in terms of importance and distribution. New incentives for tidal ecosystem management are expanding boundaries to include algal carbon and tidal transport of alkalinity, which bring additional co-benefits to coastal waters. Using examples from the conterminous USA on blue carbon stocks, radiative balance, and extent, this chapter explores timelines of physical and biogeochemical stressors and their application to past, current, and future climate mitigation functions of coastal ecosystems.

Book chapter↗

USGS2009

A Holocene record of climate-driven shifts in coastal carbon sequestration

A sediment core collected in the mesohaline portion of Chesapeake Bay was found to contain periods of increased delivery of refractory black carbon (BC) and polycyclic aromatic hydrocarbons (PAHs). The BC was most likely produced by biomass combustion during four centennialscale dry periods as indicated by the Palmer Drought Severity Index (PDSI), beginning in the late Medieval Warm Period of 1100 CE. In contrast, wetter periods were associated with increased non-BC organic matter influx into the bay, likely due to greater runoff and associated nutrient delivery. In addition, an overall increase in both BC and non-BC organic matter deposition during the past millennium may reflect a shift in climate regime. The finding that carbon sequestration in the coastal zone responds to climate fluctuations at both centennial and millennial scales through fire occurrence and nutrient delivery has implications for past and future climate predictions. Drought-induced fires may lead, on longer timescales, to greater carbon sequestration and, therefore, represent a negative climate feedback. Copyright 2009 by the American Geophysical Union.

Geophysical Research Letters↗

USGS2018

Climate change science and modeling

This chapter provides a brief background on climate change science, climate simulation models, and models that project the impacts of changes in climate on tree species and ecosystems. Throughout the chapter, boxes list resources for more information on each topic. A more detailed scientific review of climate change science, trends, and modeling can be found in the Intergovernmental Panel on Climate Change (IPCC) Fifth Assessment Report (IPCC 2014), and the Fourth National Climate Assessment (U.S. Global Climate Research Program [USGCRP] 2017).

Delaware, Maryland, New Jersey, New York, Pennsylv↗

USGS2014

Radiocarbon age-offsets in an arctic lake reveal the long-term response of permafrost carbon to climate change

Continued warming of the Arctic may cause permafrost to thaw and speed the decomposition of large stores of soil organic carbon (OC), thereby accentuating global warming. However, it is unclear if recent warming has raised the current rates of permafrost OC release to anomalous levels or to what extent soil carbon release is sensitive to climate forcing. Here we use a time series of radiocarbon age-offsets ( 14 C) between the bulk lake sediment and plant macrofossils deposited in an arctic lake as an archive for soil and permafrost OC release over the last 14,500 years. The lake traps and archives OC imported from the watershed and allows us to test whether prior warming events stimulated old carbon release and heightened age-offsets. Today, the age-offset (2 ka; thousand of calibrated years before A.D. 1950) and the depositional rate of ancient OC from the watershed into the lake are relatively low and similar to those during the Younger Dryas cold interval (occurring 12.9–11.7 ka). In contrast, age-offsets were higher (3.0–5.0 ka) when summer air temperatures were warmer than present during the Holocene Thermal Maximum (11.7–9.0 ka) and Bølling-Allerød periods (14.5–12.9 ka). During these warm times, permafrost thaw contributed to ancient OC depositional rates that were ~10 times greater than today. Although permafrost OC was vulnerable to climate warming in the past, we suggest surface soil organic horizons and peat are presently limiting summer thaw and carbon release. As a result, the temperature threshold to trigger widespread permafrost OC release is higher than during previous warming events.

Alaska↗

USGS2015

Pollen and spores of terrestrial plants

Pollen and spores are valuable tools in reconstructing past sea level and climate because of their ubiquity, abundance, and durability as well as their reciprocity with source vegetation to environmental change (Cronin, 1999; Traverse, 2007; Willard and Bernhardt, 2011). Pollan is found in many sedimentary environments, from freshwater to saltwater, terrestrial to marine. It can be abundant in a minimal amount of sample material, for example half a gram, as concentrations can be as high as four million grains per gram (Traverse, 2007). The abundance of pollen in a sample lends it to robust statistical analysis for the quantitative reconstruction of environments. The outer cell wall is resistant to decay in sediments and allows palynomorphs (pollen and spores) to record changes in plant communities and sea level over millions of years. These characteristics make pollen and spores a powerful tool to use in sea-level research. This chapter describes the biology of pollen and spores and how they are transported and preserved in sediments. We present a methodology for isolating pollen from sediments and a general language and framework to identify pollen as well as light micrographs of a selection of common pollen grains, We then discuss their utility in sea-level research.

Book chapter↗

USGS2023

Modeling impacts of saltwater intrusion on methane and nitrous oxide emissions in tidal forested wetlands

Emissions of methane (CH 4 ) and nitrous oxide (N 2 O) from soils to the atmosphere can offset the benefits of carbon sequestration for climate change mitigation. While past study has suggested that both CH 4 and N 2 O emissions from tidal freshwater forested wetlands (TFFW) are generally low, the impacts of coastal droughts and drought-induced saltwater intrusion on CH 4 and N 2 O emissions remain unclear. In this study, a process-driven biogeochemistry model, Tidal Freshwater Wetland DeNitrification-DeComposition (TFW-DNDC) was applied to examine the responses of CH 4 and N 2 O emissions to episodic drought-induced saltwater intrusion in TFFW along the Waccamaw River and Savannah River, USA. These sites encompass landscape gradients of both surface and porewater salinity as influenced by Atlantic Ocean tides superimposed on periodic droughts. Surprisingly, CH 4 and N 2 O emission responsiveness to coastal droughts and drought-induced saltwater intrusion varied greatly between river systems and among local geomorphologic settings. This reflected the complexity of wetland CH 4 and N 2 O emissions and suggests that simple linkages to salinity may not always be relevant, as non-linear relationships dominated our simulations. Along the Savannah River, N 2 O emissions in the moderate-oligohaline tidal forest site tended to increase dramatically under the drought condition, while CH 4 emission decreased. For the Waccamaw River, emissions of both CH 4 and N 2 O in the moderate-oligohaline tidal forest site tended to decrease under the drought condition, but the capacity of the moderate-oligohaline tidal forest to serve as a carbon sink was substantially reduced due to significant declines in net primary productivity and soil organic carbon sequestration rates as salinity killed the dominant freshwater vegetation. These changes in fluxes of CH 4 and N 2 O reflect crucial synergistic effects of soil salinity and water level on C and N dynamics in TFFW due to drought-induced seawater intrusion.

Ecological Applications↗

USGS2025

Expanding barriers: Impassable gaps interior to distribution of an isolated mountain-dwelling species

Global change is expected to expand and shrink species' distributions in complex ways beyond just retraction at warm edges and expansion at cool ones. Detecting these changes is complicated by the need for robust baseline data for comparison. For instance, gaps in species' distributions may reflect long-standing patterns, recent shifts, or merely insufficient sampling effort. We investigated an apparent gap in the distribution of the American pika, Ochotona princeps , along the North American Sierra Nevada. Historical records from this region are sparse, with ~100 km separating previously documented pika-occupied sites. Surveys during 2014–2023 confirmed that the gap is currently unoccupied by pikas, and evidence of past occurrence indicates that the gap has expanded over time, likely due to contemporary global change. Sites lacking evidence of past pika occurrence were climatically and geographically more distant from sites with signs of recent (former) occurrence and currently occupied sites. Formerly and currently occupied sites were partially climatically distinct, suggesting either metapopulation-like dynamics or an extinction debt that may eventually result in further population losses at the edge of suitable climate space. The Feather River gap aligns with one of several “low points” in the otherwise continuous boreal-like conditions spanning the Cascade Range and Sierra Nevada and is coincident with discontinuities in ranges of other mammals. These results highlight the potential for climate-driven fragmentation and range retraction in regions considered climatically and geographically interior to a species' overall distribution.

California↗

USGS2023

Planktic foraminifera

Planktic foraminifera are single-celled marine organisms that secrete calcium carbonate tests. They live in the ocean's photic zone, and when they die, their tests, each about the size of a grain of sand, collect on the ocean floor. The geographic distribution of planktic foraminifera is mostly governed by the temperature and salinity of the ocean surface, and species assemblages are generally arranged in latitudinal bands from polar to tropical, with more species occupying warmer waters. Their ubiquity in the world's oceans since the Cretaceous Period makes them ideal biostratigraphic markers, and their sensitivity to environmental changes makes them excellent proxies of past ecological, oceanographic and climatic history.

Book chapter↗

USGS2024

Paleosols in loess deposits

Paleosols , in loess or other deposits, are soils of the past. Three types can be recognized, buried, exhumed (once buried, but now at the surface), and relict (not buried, but formed under a different environment in the past). In loess deposits, paleosols have stratigraphic significance as they represent times of minimal or no loess accumulation. In many parts of the world, loess-derived paleosols mark interglacial periods, but in other regions, loess accumulation and soil formation are competing processes that occur together during both glacial and interglacial periods. Identification of paleosols within loess sequences can be accomplished by recognition of soil morphological properties (A and B horizons), zones of pedogenic clay accumulation, zones of carbonate loss (humid regions) or carbonate gain (arid regions), distinct phosphorus depth functions, and magnetic properties. Once recognized, paleosols can serve not only as valuable stratigraphic markers, but can help in reconstructing past environmental conditions, particularly climate and vegetation. Such goals can be accomplished by determination of degree of chemical weathering in paleosols from chemistry and mineralogy, carbon isotopic composition of paleosol organic matter, phytoliths, and magnetic properties.

Book chapter↗

USGS2012

Resource and hazard implications of gas hydrates in the Northern Gulf of Mexico: Results of the 2009 Joint Industry Project Leg II Drilling Expedition

In the 1970's, Russian scientists were the first to suggest that gas hydrates, a crystalline solid of water and natural gas, and a historical curiosity to physical chemists, should occur in abundance in the natural environment. Since this early start, the scientific foundation has been built for the realization that gas hydrates are a global phenomenon, occurring in permafrost regions of the arctic and in deep water portions of most continental margins worldwide. Recent field testing programs in the Arctic (Dallimore et al., 2008; Yamamoto and Dallimore, 2008) have indicated that natural gas can be produced from gas hydrate accumulations, particularly when housed in sand-rich sediments, with existing conventional oil and gas production technology (Collett et al., 2008) and preparations are now being made for the first marine field production tests (Masuda et al., 2009). Beyond a future energy resource, gas hydrates in some settings may represent a geohazard. Other studies also indicate that methane released to the atmosphere from destabilized gas hydrates may have contributed to global climate change in the past.

Northern Gulf Of Mexico↗

USGS2011

An analysis of modern pollen rain from the Maya lowlands of northern Belize

In the lowland Maya area, pollen records provide important insights into the impact of past human populations and climate change on tropical ecosystems. Despite a long history of regional paleoecological research, few studies have characterized the palynological signatures of lowland ecosystems, a fact which lowers confidence in ecological inferences made from palynological data. We sought to verify whether we could use pollen spectra to reliably distinguish modern ecosystem types in the Maya lowlands of Central America. We collected 23 soil and sediment samples from eight ecosystem types, including upland, riparian, secondary, and swamp ( bajo ) forests; pine savanna; and three distinct wetland communities. We analyzed pollen spectra with non-metric multidimensional scaling (NMDS), and found significant compositional differences in ecosystem types' pollen spectra. Forested sites had spectra dominated by Moraceae/Urticaceae pollen, while non-forested sites had significant portions of Poaceae, Asteraceae, and Amaranthaceae pollen. Upland, bajo , and riparian forest differed in representation of Cyperaceae, Bactris -type, and Combretaceae/Melastomataceae pollen. High percentages of pine ( Pinus ), oak ( Quercus ), and the presence of Byrsonima characterized pine savanna. Despite its limited sample size, this study provides one of the first statistical analyses of modern pollen rain in the Maya lowlands. Our results show that pollen assemblages can accurately reflect differences between ecosystem types, which may help refine interpretations of pollen records from the Maya area.

Maya lowlands↗