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At least 865 records · Page 48Linked to original sources
USGS2014

Uranium-series ages of corals, sea level history, and palaeozoogeography, Canary Islands, Spain: an exploratory study for two Quaternary interglacial periods

We present the first U-series ages of corals from emergent marine deposits on the Canary Islands. Deposits at + 20 m are 481 ± 39 ka, possibly correlative to marine isotope stage (or MIS) 11, while those at + 12 and + 8 m are 120.5 ± 0.8 ka and 130.2 ± 0.8 ka, respectively, correlative to MIS 5.5. The age, elevations, and uplift rates derived from MIS 5.5 deposits on the Canary Islands allow calculations of hypothetical palaeo-sea levels during the MIS 11 high sea stand. Estimates indicate that the MIS 11 high sea stand likely was at least + 9 m (relative to present sea level) and could have been as high as + 24 m. The most conservative estimates of palaeo-sea level during MIS 11 would require an ice mass loss equivalent to all of the modern Greenland and West Antarctic ice sheets; the more extreme estimates would require additional ice mass loss from the East Antarctic ice sheet. Extralimital southern species of mollusks, found in both MIS 11 and MIS 5.5 deposits on the Canary Islands, imply warmer-than-modern sea surface temperatures during at least a part of MIS 11 and much warmer sea surface temperatures during at least a part of MIS 5.5. Both MIS 11 and MIS 5.5 marine deposits on the Canary Islands contain extralimital northern species of mollusks as well, indicating cooler-than-present waters at times during these interglacial periods. We hypothesize that the co-occurrence of extralimital southern and northern species of marine invertebrates in the fossil record of the Canary Islands reflects its geographic location with respect to major synoptic-scale controls on climate and ocean currents. Previous interglacials may have been characterized by early, insolation-forced warming, along with northward migration of the intertropical convergence zone (ITCZ), accompanied by weakened trade winds and diminished upwelling. This allowed the arrival of extralimital southern taxa from the tropical Senegalese faunal province. During later parts of the MIS 11 and 5.5 interglacials, decreased insolation may have resulted in southward migration of the ITCZ, strengthened trade winds, and re-establishment of upwelling. Such conditions may have brought about not only local extinction of the Senegalese fauna, but allowed southward migration of the cooler-water Mediterranean fauna to the Canary Islands in the later parts of interglacials, a complex palaeoclimate record that is mirrored in the deep-sea core record.

Canary Islands↗
USGS2021

Hawai‘i forest review: Synthesizing the ecology, evolution, and conservation of a model system

As the most remote archipelago in the world, the Hawaiian Islands are home to a highly endemic and disharmonic biota that has fascinated biologists for centuries. Forests are the dominant terrestrial biome in Hawai‘i, spanning complex, heterogeneous climates across substrates that vary tremendously in age, soil structure, and nutrient availability. Species richness is low in Hawaiian forests compared to other tropical forests, as a consequence of dispersal limitation from continents and adaptive radiations in only some lineages, and forests are dominated by the widespread Metrosideros species complex. Low species richness provides a relatively tractable model system for studies of community assembly, local adaptation, and species interactions. Moreover, Hawaiian forests provide insights into predicted patterns of evolution on islands, revealing that while some evidence supports “island syndromes,” there are exceptions to them all. For example, Hawaiian plants are not as a whole less defended against herbivores, less dispersible, more conservative in resource use, or more slow-growing than their continental relatives. Clearly, more work is needed to understand the drivers, sources, and constraints on phenotypic variation among Hawaiian species, including both widespread and rare species, and to understand the role of this variation for ecological and evolutionary processes, which will further contribute to conservation of this unique biota. Today, Hawaiian forests are among the most threatened globally. Resource management failures – the proliferation of non-native species in particular – have led to devastating declines in native taxa and resulted in dominance by novel species assemblages. Conservation and restoration of Hawaiian forests now rely on managing threats including climate change, ongoing species introductions, novel pathogens, lost mutualists, and altered ecosystem dynamics through the use of diverse tools and strategies grounded in basic ecological, evolutionary, and biocultural principles. The future of Hawaiian forests thus depends on the synthesis of ecological and evolutionary research, which will continue to inform future conservation and restoration practices.

Hawaii↗
USGS2015

Isotopic geochemistry of Panama rivers

River water samples collected from 78 watersheds rivers along a 500-km transect across a Late Cretaceous-Tertiary andesitic volcanic arc terrane in west-central Panama provide a synoptic overview of riverine geochemistry, chemical denudation, and CO 2 consumption in the tropics. D/H and 18 O/ 16 O relationships indicate that bedrock dissolution of andesitic arc crust in Panama is driven by water-rock interaction with meteoric precipitation as it passes through the critical zone, with no evidence of a geothermal or hydrothermal input. Sr-isotope relationships suggest a geochemical evolution for Panama riverine waters that involves mixing of bedrock pore water with water having 87 Sr/ 86 Sr ratios between 0.7037-0.7043 and relatively high Sr-contents with waters of low Sr content that enriched in radiogenic Sr that are diluted by infiltrating rainfall to variable extents.

Procedia Earth and Planetary Science↗
USGS2017

Millennial-scale variability in the local radiocarbon reservoir age of south Florida during the Holocene

A growing body of research suggests that the marine environments of south Florida provide a critical link between the tropical and high-latitude Atlantic. Changes in the characteristics of water masses off south Florida may therefore have important implications for our understanding of climatic and oceanographic variability over a broad spatial scale; however, the sources of variability within this oceanic corridor remain poorly understood. Measurements of ΔR, the local offset of the radiocarbon reservoir age, from shallow-water marine environments can serve as a powerful tracer of water-mass sources that can be used to reconstruct variability in local-to regional-scale oceanography and hydrology. We combined radiocarbon and U-series measurements of Holocene-aged corals from the shallow-water environments of the Florida Keys reef tract (FKRT) with robust statistical modeling to quantify the millennial-scale variability in ΔR at locations with (“nearshore”) and without (“open ocean”) substantial terrestrial influence. Our reconstructions demonstrate that there was significant spatial and temporal variability in ΔR on the FKRT during the Holocene. Whereas ΔR was similar throughout the region after ∼4000 years ago, nearshore ΔR was significantly higher than in the open ocean during the middle Holocene. We suggest that the elevated nearshore ΔR from ∼8000 to 5000 years ago was most likely the result of greater groundwater influence associated with lower sea level at this time. In the open ocean, which would have been isolated from the influence of groundwater, ΔR was lowest ∼7000 years ago, and was highest ∼3000 years ago. We evaluated our open-ocean model of ΔR variability against records of local-to regional-scale oceanography and conclude that local upwelling was not a significant driver of open-ocean radiocarbon variability in this region. Instead, the millennial-scale trends in open-ocean ΔR were more likely a result of broader-scale changes in western Atlantic circulation associated with an increase in the supply of equatorial South Atlantic water to the Caribbean and shifts in the character of South Atlantic waters resulting from variation in the intensity of upwelling off the southwest coast of Africa. Because accurate estimates of ΔR are critical to precise calibrations of radiocarbon dates from marine samples, we also developed models of nearshore and open-ocean ΔR versus conventional 14 C ages that can be used for regional radiocarbon calibrations for the Holocene. Our study provides new insights into the patterns and drivers of oceanographic and hydrologic variability in the Straits of Florida and highlights the value of the paleoceanographic records from south Florida to our understanding of Holocene changes in climate and ocean circulation throughout the Atlantic.

Florida↗
USGS2010

Santa Barbara Basin diatom and silicoflagellate response to global climate anomalies during the past 2200 years

Santa Barbara Basin (SBB) diatom and silicoflagellate assemblages are quantified from a box core record spanning AD 1940-2001 and an Ocean Drilling Program Hole 893A record from ???220 BC to AD 1880. The combined relative abundance of the diatoms Fragilariopsis doliolus and Nitzschia interrupteseriata from continuous two-year sampling intervals in the box core varies with sea surface temperature (SST), suggesting its utility in SST reconstruction. The assemblage data from the ODP 893A record indicate a broad interval of generally cooler SSTs between ???AD 800 and 1350, which corresponds to the Medieval Climate Anomaly (MCA), a period of generally warmer temperatures across other regions of the northern hemisphere. The assemblages also indicate an interval of generally warmer SSTs between ???AD 1400 and 1800, a period of otherwise global cooling referred to as the Little Ice Age (LIA). The changes in assemblages of diatoms and silicoflagellates support the hypothesis that the widespread droughts of the Medieval Climate Anomaly in the Western US were associated with cooler eastern North Pacific SST. The box core assemblages have higher percentages of tropical and subtropical compared to temperate and subpolar species than the ODP samples, reflecting a response of phytoplankton communities to an unusual 20th century warming. Pseudonitzschia australis, a diatom linked with domoic acid production, begins to become more common (>3% of the diatom assemblage) in the box core only after AD 1985, suggesting a link to anthropogenic activity. ?? 2008 Elsevier Ltd and INQUA.

Quaternary International↗
USGS2011

Enhanced Late Holocene ENSO/PDO expression along the margins of the eastern North Pacific

Pacific climate is known to have varied during the Holocene, but spatial patterns remain poorly defined. This paper compiles terrestrial and marine proxy data from sites along the northeastern Pacific margins and proposes that they indicate 1) suppressed ENSO conditions during the middle Holocene between ∼8000 and 4000 cal BP with a North Pacific that generally resembled a La Niña-like or more negative PDO phase and 2) a climate transition between ∼4200 and 3000 cal BP that appears to be the teleconnected expression to a more modern-like ENSO Pacific. Compared to modern day conditions, the compiled data suggest that during the middle Holocene, the Aleutian Low was generally weaker during the winter and/or located more to the west, while the North Pacific High was stronger during the summer and located more to the north. Coastal upwelling off California was more enhanced during the summer and fall but suppressed during the spring. Oregon and California sea surface temperatures (SSTs) were cooler. The Santa Barbara Basin had an anomalous record, suggesting warmer SSTs. Late Holocene records indicate a more variable, El Niño-like, and more positive PDO Pacific. The Aleutian Low became more intensified during the winter and/or located more to the east. The North Pacific High became weaker and/or displaced more to the south. Coastal upwelling off California intensified during the spring but decreased during the fall. Oregon and California SSTs became warmer, recording the shoreward migration of sub-tropical gyre waters during the fall, while spring upwelling (cooler SST) increased in the Santa Barbara Basin. The high-resolution proxy records indicate enhanced ENSO and PDO variability after ∼4000 cal BP off southern California, ∼3400 cal BP off northern California, and by ∼2000 cal BP in southwestern Yukon. A progressively northward migration of the ENSO teleconnection during the late Holocene is proposed.

Quaternary International↗
USGS2004

Glacial-interglacial organic carbon record from the Makassar Strait, Indonesia: Implications for regional changes in continental vegetation

Recent studies convincingly show that climate in the Western Pacific Warm Pool and other equatorial/tropical regions was significantly colder (by ???3-4??C) during glacial periods, prompting a reexamination of the late Pleistocene paleoenvironments of these regions. This study examines changes in continental vegetation during the last two deglaciations (Terminations I and II) using a sediment core (MD9821-62) recovered from the Makassar Strait, Indonesia. Evidence based on the lignin phenol ratios suggests that vegetation on Borneo and other surrounding islands did not significantly change from tropical rainforest during the last two glacial periods relative to subsequent interglacial periods. This supports the hypothesis that the winter monsoon increased in strength during glacial periods, allowing Indonesia to maintain high rainfall despite the cooler conditions. ?? 2003 Elsevier Ltd. All rights reserved.

Quaternary Science Reviews↗
USGS2009

Evidence for prolonged El Nino-like conditions in the Pacific during the Late Pleistocene: a 43 ka noble gas record from California groundwaters

Information on the ocean/atmosphere state over the period spanning the Last Glacial Maximum - from the Late Pleistocene to the Holocene - provides crucial constraints on the relationship between orbital forcing and global climate change. The Pacific Ocean is particularly important in this respect because of its dominant role in exporting heat and moisture from the tropics to higher latitudes. Through targeting groundwaters in the Mojave Desert, California, we show that noble gas derived temperatures in California averaged 4.2 ?? 1.1 ??C cooler in the Late Pleistocene (from ???43 to ???12 ka) compared to the Holocene (from ???10 to ???5 ka). Furthermore, the older groundwaters contain higher concentrations of excess air (entrained air bubbles) and have elevated oxygen-18/oxygen-16 ratios (?? 18 O) - indicators of vigorous aquifer recharge, and greater rainfall amounts and/or more intense precipitation events, respectively. Together, these paleoclimate indicators reveal that cooler and wetter conditions prevailed in the Mojave Desert from ???43 to ???12 ka. We suggest that during the Late Pleistocene, the Pacific ocean/atmosphere state was similar to present-day El Nino-like patterns, and was characterized by prolonged periods of weak trade winds, weak upwelling along the eastern Pacific margin, and increased precipitation in the southwestern U.S.

Quaternary Science Reviews↗
USGS2015

The Holocene history of the North American Monsoon: 'known knowns' and 'known unknowns' in understanding its spatial and temporal complexity

Evidence for climatic change across the North American Monsoon (NAM) and adjacent areas is reviewed, drawing on continental and marine records and the application of climate models. Patterns of change at 12,000, 9000, 6000 and 4000 cal yr BP are presented to capture the nature of change from the Younger Dryas (YD) and through the mid-Holocene. At the YD, conditions were cooler overall, wetter in the north and drier in the south, while moving into the Holocene wetter conditions became established in the south and then spread north as the NAM strengthened. Until c. 8000 cal yr BP, the Laurentide Ice Sheet influenced precipitation in the north by pushing the Bermuda High further south. The peak extent of the NAM seems to have occurred around 6000 cal yr BP. 4000 cal yr BP marks the start of important changes across the NAM region, with drying in the north and the establishment of the clear differences between the summer-rain dominated south and central areas and the north, where winter rain is more important. This differentiation between south and north is crucial to understanding many climate responses across the NAM. This increasing variability is coincident with the declining influence of orbital forcing. 4000 cal yr BP also marks the onset of significant anthropogenic activity in many areas. For the last 2000 years, the focus is on higher temporal resolution change, with strong variations across the region. The Medieval Climate Anomaly (MCA) is characterised by centennial scale ‘megadrought’ across the southwest USA, associated with cooler tropical Pacific SSTs and persistent La Niña type conditions. Proxy data from southern Mexico, Central America and the Caribbean reveal generally wetter conditions, whereas records from the highlands of central Mexico and much of the Yucatan are typified by long -term drought. The Little Ice Age (LIA), in the north, was characterised by cooler, wetter winter conditions that have been linked with increased frequency of El Niño's. Proxy records in the central and southern regions reveal generally dry LIA conditions, consistent with cooler SSTs in the Caribbean and Gulf of Mexico. This synthesis demonstrates that in some periods, one major forcing can dominate across the whole area (e.g. insolation in the early-mid Holocene), but at other times there is strong variability in patterns of change due to the differential impact of forcings such as the Pacific Decadal Oscillation (PDO) and the Atlantic Multidecadal Oscillation (AMO) on precipitation seasonality.

Quaternary Science Reviews↗
USGS2016

Teleconnected ocean forcing of Western North American droughts and pluvials during the last millennium

Western North America (WNA) is rich in hydroclimate reconstructions, yet questions remain about the causes of decadal-to-multidecadal hydroclimate variability. Teleconnection patterns preserved in annually-resolved tree-ring reconstructed drought maps, and anomalies in a global network of proxy sea surface temperature (SST) reconstructions, were used to reassess the evidence linking ocean forcing to WNA hydroclimate variability over the past millennium. Potential forcing mechanisms of the Medieval Climate Anomaly (MCA) and individual drought and pluvial events—including two multidecadal-length MCA pluvials—were evaluated. We show strong teleconnection patterns occurred during the driest (wettest) years within persistent droughts (pluvials), implicating SSTs as a potent hydroclimate forcing mechanism. The role of the SSTs on longer timescales is more complex. Pacific teleconnection patterns show little long-term change, whereas low-resolution SST reconstructions vary over decades to centuries. While weaker than the tropical Pacific teleconnections, North Atlantic teleconnection patterns and SST reconstructions also show links to WNA droughts and pluvials, and may in part account for longer-term WNA hydroclimate changes. Nonetheless, evidence linking WNA hydroclimate to SSTs still remains sparse and nuanced—especially over long-timescales with a broader range of hydroclimatic variability than characterized during the 20th century.

Quaternary Science Reviews↗
USGS2019

Radiocarbon and geologic evidence reveal Ilopango volcano as source of the colossal 'mystery' eruption of 539/40 CE

Ilopango volcano (El Salvador) erupted violently during the Maya Classic Period (250–900 CE) in a densely-populated and intensively-cultivated region of the southern Maya realm, causing regional abandonment of an area covering more than 20,000 km 2 . However, neither the regional nor global impacts of the Tierra Blanca Joven (TBJ) eruption in Mesoamerica have been well appraised due to limitations in available volcanological, chronological, and archaeological observations. Here we present new evidence of the age, magnitude and sulfur release of the TBJ eruption, establishing it as one of the two hitherto unidentified volcanic triggers of a period of stratospheric aerosol loading that profoundly impacted Northern Hemisphere climate and society between circa 536 and 550 CE. Our chronology is derived from 100 new radiocarbon measurements performed on three subfossil tree trunks enveloped in proximal TBJ pyroclastic deposits. We also reassess the eruption magnitude using terrestrial (El Salvador, Guatemala, Honduras) and near-shore marine TBJ tephra deposit thickness measurements. Together, our new constraints on the age, eruption size (43.6 km 3 Dense Rock Equivalent of magma, magnitude = 7.0) and sulfur yield (∼9–90 Tg), along with Ilopango's latitude (13.7° N), squarely frame the TBJ as the major climate-forcing eruption of 539 or 540 CE identified in bipolar ice cores and sourced to the tropics. In addition to deepening appreciation of the TBJ eruption's impacts in Mesoamerica, linking it to the major Northern Hemisphere climatic downturn of the mid-6th century CE offers another piece in the puzzle of understanding Eurasian history of the period.

Guazapa↗
USGS2022

Contrasting Common Era climate and hydrology sensitivities from paired lake sediment dinosterol hydrogen isotope records in the South Pacific Convergence Zone

Hydroclimate on ‘Uvea (Wallis et Futuna) is controlled by rainfall associated with the South Pacific Convergence Zone (SPCZ), the southern hemisphere's largest precipitation feature. To extend the short observational precipitation record, the hydrogen isotopic composition of the algal lipid biomarker dinosterol (δ 2 H dinosterol ) was measured in sediment cores from two volcanic crater lakes on ‘Uvea. The modern lakes differ morphologically and chemically but both contain freshwater within the photic zone, support phytoplankton communities inclusive of dinosterol-producing dinoflagellates, and experience identical climate conditions. δ 2 H dinosterol values track lake water isotope ratios, ultimately controlled in the tropics by precipitation amount and evaporative enrichment. However, in 88-m-deep Lac Lalolalo a steadily decreasing trend in sedimentary δ 2 H dinosterol values from −227‰ around year 988 CE to modern values as low as −303‰, suggests this lake's evolution from an active volcanic setting to the present system strongly influenced δ 2 H dinosterol values. Although current hydrology and water isotope systematics may now reflect precipitation and evaporation in this lake, the interaction between these processes and large changes in basin morphology, geochemistry, and hydrology obstruct the recovery of a climate signal from Lac Lalolalo's sedimentary δ 2 H dinosterol records. This work emphasizes the importance of site replication and the use of complementary climate reconstruction tools, especially when using molecular proxies that may be sensitive to more than one environmental parameter. Contrary to its neighbor, duplicate δ 2 H dinosterol records from 23-m-deep Lac Lanutavake varied between −277‰ and −297‰ and indicate slightly drier conditions during the time-period known as the Medieval Climate Anomaly (MCA, 950–1250 CE). The δ 2 H dinosterol signal in Lac Lanutavake was muted compared to published records from ‘Upolu (Samoa) and Efate (Vanuatu) indicating that ‘Uvea's location is not as sensitive to precipitation variability at sites farther from the SPCZ central axis. Lithogenic runoff proxies combined with δ 2 H dinosterol support the interpretation of a relatively dry MCA on ‘Uvea, ‘Upolu, and Efate, potentially due to less intense precipitation, a contracted, or a more zonally oriented SPCZ.

Efate Island, Lac Lalolalo, Lac Lanoto'o, Lac Lanu↗
USGS2022

Seasonality of precipitation in the southwestern United States during the late Pleistocene inferred from stable isotopes in herbivore tooth enamel

The late Pleistocene was a climatically dynamic period, with abrupt shifts between cool-wet and warm-dry conditions. Increased effective precipitation supported large pluvial lakes and long-lived spring ecosystems in valleys and basins throughout the western and southwestern U.S., but the source and seasonality of the increased precipitation are debated. Increases in the proportions of C 4 /(C 4 + C 3 ) grasses in the diets of large grazers have been ascribed both to increases in summer precipitation and lower atmospheric CO 2 levels. Here we present stable carbon and oxygen isotope data from tooth enamel of late Pleistocene herbivores recovered from paleowetland deposits at Tule Spring Fossil Beds National Monument in the Las Vegas Valley of southern Nevada, as well as modern herbivores from the surrounding area. We use these data to investigate whether winter or summer precipitation was responsible for driving the relatively wet hydroclimate conditions that prevailed in the region during the late Pleistocene. We also evaluate whether late Pleistocene grass C 4 /(C 4 + C 3 ) was higher than today, and potential drivers of any changes. Tooth enamel δ 18 O values for Pleistocene Equus , Bison , and Mammuthus are generally low (average 22.0 ± 0.7‰, 2 s.e., VSMOW) compared to modern equids (27.8 ± 1.5‰), and imply lower water δ 18 O values (−16.1 ± 0.8‰) than modern precipitation (−10.5‰) or in waters present in active springs and wells in the Las Vegas Valley (−12.9‰), an area dominated by winter precipitation. In contrast, tooth enamel of Camelops (a browser) generally yielded higher δ 18 O values (23.9 ± 1.1‰), possibly suggesting drought tolerance. Mean δ 13 C values for the Pleistocene grazers (−6.6 ± 0.7‰, 2 s.e., VPDB) are considerably higher than for modern equids (−9.6 ± 0.4‰) and indicate more consumption of C 4 grass (17 ± 5%) than today (4 ± 4%). However, calculated C 4 grass consumption in the late Pleistocene is strikingly lower than the proportion of C 4 grass taxa currently present in the valley (55–60%). δ 13 C values in Camelops tooth enamel (−7.7 ± 1.0‰) are interpreted as reflecting moderate consumption (14 ± 8%) of Atriplex (saltbush), a C 4 shrub that flourishes in regions with hot, dry summers. Lower water δ 18 O values, lower abundance of C 4 grasses, and the inferred presence of Atriplex are all consistent with general circulation models for the late Pleistocene that show enhanced delivery of winter precipitation, sourced from the north Pacific, into the interior western U.S. but do not support alternative models that infer enhanced delivery of summer precipitation, sourced from the tropics. In addition, we hypothesize that dietary competition among the diverse and abundant Pleistocene fauna may have driven the grazers analyzed here to feed preferentially on C 4 grasses. Dietary partitioning, especially when combined with decreased p CO2 levels during the late Pleistocene, can explain the relatively high δ 13 C values observed in late Pleistocene grazers in the Las Vegas Valley and elsewhere in the southwestern U.S. without requiring additional summer precipitation. Pleistocene hydroclimate parameters derived from dietary and floral records may need to be reevaluated in the context of the potential effects of dietary preferences and lower p CO2 levels on the stability of C 3 vs. C 4 plants.

Nevada↗
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↗
USGS2010

Global estimates of evapotranspiration and gross primary production based on MODIS and global meteorology data

The simulation of gross primary production (GPP) at various spatial and temporal scales remains a major challenge for quantifying the global carbon cycle. We developed a light use efficiency model, called EC-LUE, driven by only four variables: normalized difference vegetation index (NDVI), photosynthetically active radiation (PAR), air temperature, and the Bowen ratio of sensible to latent heat flux. The EC-LUE model may have the most potential to adequately address the spatial and temporal dynamics of GPP because its parameters (i.e., the potential light use efficiency and optimal plant growth temperature) are invariant across the various land cover types. However, the application of the previous EC-LUE model was hampered by poor prediction of Bowen ratio at the large spatial scale. In this study, we substituted the Bowen ratio with the ratio of evapotranspiration (ET) to net radiation, and revised the RS-PM (Remote Sensing-Penman Monteith) model for quantifying ET. Fifty-four eddy covariance towers, including various ecosystem types, were selected to calibrate and validate the revised RS-PM and EC-LUE models. The revised RS-PM model explained 82% and 68% of the observed variations of ET for all the calibration and validation sites, respectively. Using estimated ET as input, the EC-LUE model performed well in calibration and validation sites, explaining 75% and 61% of the observed GPP variation for calibration and validation sites respectively. Global patterns of ET and GPP at a spatial resolution of 0.5° latitude by 0.6° longitude during the years 2000–2003 were determined using the global MERRA dataset (Modern Era Retrospective-Analysis for Research and Applications) and MODIS (Moderate Resolution Imaging Spectroradiometer). The global estimates of ET and GPP agreed well with the other global models from the literature, with the highest ET and GPP over tropical forests and the lowest values in dry and high latitude areas. However, comparisons with observed GPP at eddy flux towers showed significant underestimation of ET and GPP due to lower net radiation of MERRA dataset. Applying a procedure to correct the systematic errors of global meteorological data would improve global estimates of GPP and ET. The revised RS-PM and EC-LUE models will provide the alternative approaches making it possible to map ET and GPP over large areas because (1) the model parameters are invariant across various land cover types and (2) all driving forces of the models may be derived from remote sensing data or existing climate observation networks.

Remote Sensing of Environment↗
USGS2024

Tracking mangrove condition changes using dense Landsat time series

Mangroves in tropical and subtropical coasts are subject to episodic disturbances, notably from severe storms, leading to potential widespread vegetation mortality. The ability of vegetation to recover varies, and with disturbances becoming more frequent and severe, it is vital to track and project vegetation responses to support management and policy decisions. Prior studies have largely focused on binary mangrove mapping (i.e., presence or absence), while tracking conditions and condition change have not received sufficient attention. In this paper, we demonstrate a method based on dense time series Landsat images for continuous monitoring of mangrove conditions, where we track three kinds of post-disturbance mangrove conditions, including disturbed (disturbed, with rebound to the previous state within one growing season), recovering (undergoing natural recovery in longer than one growing season), and declining (showing long-term decline after disturbance). The method starts with disturbance detection using the DEtection and Characterization Of the tiDal wEtland change (DECODE) algorithm, an existing dense time series model designed to detect disturbances in tidal wetlands with adaptation to tidal fluctuations. This algorithm is well suited for the detection of tidal wetland disturbances but does not provide satisfactory post-disturbance monitoring results, due to the substantial variability in post-disturbance Landsat observations. To better monitor post-disturbance conditions, a new time series fitting approach, DECODER (DECODE and Recovery), is proposed for the recovery stage. Additionally, for temporal segments divided by disturbance events, we built a random forest classifier with temporal-spectral variables derived from the time series model to characterize mangrove conditions. Employing this approach in Florida's mangroves, we generated condition maps, such as dieback and recovery, with an overall accuracy of approximately 97.96 ± 0.86- [95 % confidence intervals]. Comparing post-hurricane conditions in Florida revealed that the increased frequency and severity of disturbances are challenging mangrove resilience, potentially diminishing their ability to recover and sustain ecosystem functions.

Florida↗
USGS2019

Life history, genetics, range expansion and new frontiers of the lionfish (Pterois volitans, Perciformes: Pteroidae) in Latin America

Pterois volitans (lionfish) is a midsize predatory fish commonly found in waters of the western Pacific and Indian Ocean. The species was first documented in Dania Beach, Florida (northwestern Caribbean) in 1985. Since that time the species has expanded its range rapidly to the Northwestern Atlantic Ocean, Gulf of Mexico, and Caribbean Sea. Since its introduction P. volitans has changed community structure and biodiversity of Caribbean reef communities and other coastal tropical ecosystems. Continuous introductions (accidental or intentional), limited natural predators, naïve-range prey behavior, high predation rates on competitors, continuous reproduction, and an extended period of larval dispersal have been the keys for successful invasion and rapid range extension of P. volitans . This invasion has become so severe that it has been recognized as one of the world’s top conservation issues. Here, we review the life history, behavior, and historical and contemporary genetic patterns that facilitate expansion and the colonization process. A greater understanding of lionfish biology, ecology, and the changes related to its present condition as a super-invader could improve current and future management strategies and new detection and response methodologies. We also examine new invasion frontiers that this species has the potential to colonize such as the eastern Pacific. This information will provide managers, the scientific community, and the civil society better tools for eradication, control and management of future invasions of this and other invasive species.

Caribbean Sea, Latin America↗