Timme H. Donders

A novel approach for developing high-resolution sub-fossil peat chronologies with 14C dating

Sub-fossil sections from a Florida wetland were accelerator mass spectrometry (AMS) dated and the sedimen- tological conditions were determined. 14C data were calibrated using a combined wiggle-match and 14C bomb-pulse approach. Repeatable results were obtained providing accurate peat chronologies for the last 130 calendar yr. Assessment of the different errors involved led to age models with 3-5 yr precision. This allows direct calibration of paleoenvironmental proxies with meteorological data. The time frame in which 14C dating is commonly applied can possibly be extended to include the 20th century.

Orbitally forced Azolla blooms And Middle Eocene Arctic hydrology: Clues from palynology

The high abundances and cyclic distribution of remains of the freshwater fern Azolla in early-Middle Eocene sediments from the Arctic Ocean have previously been related to episodic surface-water freshening, which was speculated to be orbitally modulated. Our integrated palynological and cyclostratigraphical analysis of the recovered Azolla interval in Integrated Ocean Drilling Program (IODP) core 302-M0004A-11X resulted in the recognition of two clear periodicities: a dominant ~1.2 m cyclicity, which we relate to changes in obliquity (~40 k.y.), and a weaker ~0.7 m cyclicity, which we link to precession (~21 k.y.). Cycles in the abundances of Azolla, cysts of freshwater-tolerant dinoflagellates, and swamp-vegetation pollen show covariability in the obliquity domain. This strong correlation suggests periods of enhanced rainfall and runoff during Azolla blooms, presumably linked to increased local summer temperatures during obliquity maxima. Larix and bisaccate conifer pollen covary at the precession frequency, with peak occurrences corresponding to precession minima, possibly as a result of enhanced continental runoff from a more remote source area and a stronger seasonal contrast. Following the sudden demise of Azolla ca. 48.1 Ma, runoff (cycles) continued to influence the central Arctic at decreased intensity. This and a concomitant decline in swamp-vegetation pollen suggest edaphically drier conditions on land and decreased runoff into the Arctic Ocean, causing salinity changes, which might have been fatal for Azolla. Moreover, a sea-level rise, inferred from overall decreasing total terrestrial palynomorph concentrations, possibly facilitated oceanic connections.

Three‐hundred‐year hydrological changes in a subtropical estuary, Rookery Bay (Florida): Human impact versus natural variability

The coastal wetland ecosystems in Florida are highly sensitive to changes in freshwater budget, which is driven by regional sea surface temperature, tropical storm activity, and the El Nino-Southern Oscillation (ENSO). Although studying Florida wetlands is pivotal to the understanding of these interacting climate systems, wetland dynamics have been severely altered by recent land use and drainage activities. To gather insights into the natural variability of the coastal ecosystems in Florida versus the effects of anthropogenic impact in the area, we present a 300-year record of changes in the hydrological cycle from a shallow subtropical estuary (Rookery Bay) on the western shelf of Florida, Gulf of Mexico. Palynological (pollen and organic-walled dinoflagellate cysts), diatom, and sedimentological analyses of a sediment core reveal significant changes in past runoff and wetland development. The onset and development of human impact in Florida are evident from high influx of Ambrosia pollen at about A.D. 1900, indicative of land clearance and disturbed conditions. To date, this is the southernmost record of Ambrosia increase related to human impact in the United States. Wetland drainage and deforestation since A.D. 1900 are evident from the reduced freshwater wetland and pine vegetation, and lower abundances of phytoplankton species indicative of lagoonal and brackish conditions. High runoff after A.D. 1900 relates to increased erosionand may correspondingly reflect higher impact from hurricane landfalls in SW Florida. Several phases with high siliciclastic input and greater wetland pollen abundance occur that predate the human impact period. These phases are interpreted as periods with higher runoff and are likely related to regional longer-term climate variability. Copyright 2008 by the American Geophysical Union.

ENSO signature in botanical proxy time series extends terrestrial El Niño record into the (sub)tropics

[1] The El Nino–Southern Oscillation (ENSO) exerts significant control over the amount of Florida winter precipitation. We use a local near-annual resolved palaeobotanical proxy record from southern Florida to test for historic ENSO variability over the past 125years. Palaeobotanical proxies from a Florida wetland, pollen counts, and a new drought-stress proxy based on leaf epidermal cell densities are used as indicators of moisture availability during the winter growing season. Spectral analysis and band-pass filtering of the proxy records reveal significant variability within the 2–7year bandwidth characteristic of ENSO, as well as decadal signatures. A maximum likelihood palaeoprecipitation reconstruction of the pollen record based on modern vegetation distributions shows values and variability comparable to instrumental records. The approach shows the dominant control of ENSO on Florida vegetation and provides a powerful means to detect discrete ENSO variability in older intervals. Citation: Donders, T. H., S. W. Punyasena, H. J. de Boer, and F. Wagner-Cremer (2013), ENSO signature in botanical proxy time series extends terrestrial El Nino record into the (sub)tropics, Geophys. Res. Lett., 40 ,5 776–5781, doi:10.1002/2013GL058038.

Drought stress signals in modern and subfossil Quercus laurifolia (Fagaceae) leaves reflect winter precipitation in southern Florida tied to El Niño–Southern Oscillation activity

In the present study, structural xeromorphic features in modern and subfossil Quercus laurifolia leaves from southern Florida were quantified to reconstruct past precipitation changes in sensitive terrestrial settings. Absolute cell numbers/mm(2), quantified as epidermal cell density (ED) have been analyzed on leaves from herbarium collections as well as the leaves accumulated during the past 125 years in peat deposits. The results reveal a common principal correlation between the measured ED and winter precipitation (November through March, NDJFM: Herbarium r = -0.74; peat profiles FAK98 r = -0.72, FAK02 r = -0.53) providing a measure of seasonal drought stress. In Florida, the amount of winter precipitation depends on El Niño-Southern Oscillation (ENSO) activity, where El Niño years produce wet and cold winters, while La Niña winters are dry and warm. The negative correlation between cell numbers and winter precipitation has the potential to record precipitation variability from subfossil leaves on near-annual to decadal time scales. In subtropical, terrestrial environments, where traditional paleo-proxies are limited, systematic analysis of leaf morphological characteristics can provide important information on precipitation changes through time.

Multi-Year Leaf-Level Response to Sub-Ambient and Elevated Experimental CO2 in Betula nana

The strong link between stomatal frequency and CO2 in woody plants is key for understanding past CO2 dynamics, predicting future change, and evaluating the significant role of vegetation in the hydrological cycle. Experimental validation is required to evaluate the long-term adaptive leaf response of C3 plants to CO2 conditions; however, studies to date have only focused on short-term single-season experiments and may not capture (1) the full ontogeny of leaves to experimental CO2 exposure or (2) the true adjustment of structural stomatal properties to CO2, which we postulate is likely to occur over several growing seasons. We conducted controlled growth chamber experiments at 150 ppmv, 450 ppmv and 800 ppmv CO2 with woody C3 shrub Betula nana (dwarf birch) over two successive annual growing seasons and evaluated the structural stomatal response to atmospheric CO2 conditions. We find that while some adjustment of leaf morphological and stomatal parameters occurred in the first growing season where plants are exposed to experimental CO2 conditions, amplified adjustment of non-plastic stomatal properties such as stomatal conductance occurred in the second year of experimental CO2 exposure. We postulate that the species response limit to CO2 of B. nana may occur around 400–450 ppmv. Our findings strongly support the necessity for multi-annual experiments in C3 perennials in order to evaluate the effects of environmental conditions and provide a likely explanation of the contradictory results between historical and palaeobotanical records and experimental data.

First Steps Toward Maturing the Shallow Gas Play - Results of an Integrated Exploration Workflow

Recent exploration activities in two of the largest deltas in the world, the still active Nile delta and the Cenozoic Southern North Sea (SNS) deltas, proved the potential of shallow gas resources. Although, previously seen as a hazard or an exploration tool for deeper hydrocarbons, the shallow gas accumulations may represent a valuable additional hydrocarbon resource, especially if located near existing infrastructures. Nonetheless, shallow gas production is still limited due to a lack of insight in the petroleum system. Knowledge on the geological conditions that enable accumulation of shallow gas is essential since gas at these depths is highly buoyant, and tends to migrate towards the surface. Furthermore, the nature of these accumulations depends on the type of sediment and the anatomy of the delta they reside in. In order to mature the shallow gas play, a multidisciplinary workflow was applied to the SNS delta that involves 1) the reconstruction of the internally complex delta body, 2) a combined deterministic/stochastic approach to make reservoir property predictions, 3) evaluation of the HC origin, and 4) a grain-size based method to predict the seal-integrity of the sealing clay layers. The results include a first evaluation of the potential of shallow HC accumulations in terms of trapping geometry, seal capacity, sourcing and migration. The presented workflow is applicable to areas where limited exploration data is available, but where critical production data is (still) missing. By reviewing the HC systems of the Nile and SNS deltas many similarities emerge that are expressed by 1) the control of sea-level and climate on the distribution of reservoirs, seals and organic material, 2) the presence of stratigraphic traps and 3) the role of deeper salt and faults in the formation of structural traps. For both settings, the origin of the shallow gas may be deep subsurface thermogenic sources or biogenic sources in shallower strata, or a mixture. To date, reserve estimates for the shallow gas play are often hard to make using conventional exploration techniques due to the inability to discriminate high vs. low saturation shallow gas. The potential of pre-stack seismic inversions or other geophysical techniques such as CSEM appear essential in maturing the Shallow Gas play. Copyright 2014, International Petroleum Technology Conference. ConocoPhillips; et al.; ExxonMobil; Maersk Oil; Qatar Petroleum; Shell

Region-Specific Sensitivity of Anemophilous Pollen Deposition to Temperature and Precipitation

Understanding relations between climate and pollen production is important for several societal and ecological challenges, importantly pollen forecasting for pollinosis treatment, forensic studies, global change biology, and high-resolution palaeoecological studies of past vegetation and climate fluctuations. For these purposes, we investigate the role of climate variables on annual-scale variations in pollen influx, test the regional consistency of observed patterns, and evaluate the potential to reconstruct high-frequency signals from sediment archives. A 43-year pollen-trap record from the Netherlands is used to investigate relations between annual pollen influx, climate variables (monthly and seasonal temperature and precipitation values), and the North Atlantic Oscillation climate index. Spearman rank correlation analysis shows that specifically in Alnus, Betula, Corylus, Fraxinus, Quercus and Plantago both temperature in the year prior to (T-1), as well as in the growing season (T), are highly significant factors (TApril rs between 0.30 [P<0.05[ and 0.58 [P<0.0001]; TJuli-1 rs between 0.32 [P<0.05[ and 0.56 [P<0.0001]) in the annual pollen influx of wind-pollinated plants. Total annual pollen prediction models based on multiple climate variables yield R2 between 0.38 and 0.62 (P<0.0001). The effect of precipitation is minimal. A second trapping station in the SE Netherlands, shows consistent trends and annual variability, suggesting the climate factors are regionally relevant. Summer temperature is thought to influence the formation of reproductive structures, while temperature during the flowering season influences pollen release. This study provides a first predictive model for seasonal pollen forecasting, and also aides forensic studies. Furthermore, variations in pollen accumulation rates from a sub-fossil peat deposit are comparable with the pollen trap data. This suggests that high frequency variability pollen records from natural archives reflect annual past climate variability, and can be used in palaeoecological and -climatological studies to bridge between population- and species-scale responses to climate forcing.

Forensic Comparison of Soil Samples Using Nondestructive Elemental Analysis

Soil can play an important role in forensic cases in linking suspects or objects to a crime scene by comparing samples from the crime scene with samples derived from items. This study uses an adapted ED‐XRF analysis (sieving instead of grinding to prevent destruction of microfossils) to produce elemental composition data of 20 elements. Different data processing techniques and statistical distances were evaluated using data from 50 samples and the log‐LR cost (Cllr). The best performing combination, Canberra distance, relative data, and square root values, is used to construct a discriminative model. Examples of the spatial resolution of the method in crime scenes are shown for three locations, and sampling strategy is discussed. Twelve test cases were analyzed, and results showed that the method is applicable. The study shows how the combination of an analysis technique, a database, and a discriminative model can be used to compare multiple soil samples quickly.

Towards a Better Understanding of Shallow Seismic Anomalies in the Dutch Offshore

Recent exploration and production activities in the Cenozoic Southern North Sea (SNS) deltas, proved the economic potential of shallow gas resources, especially if located near existing infrastructures. Nonetheless, shallow gas production is still limited due to a lack of insight in the petroleum system, especially with respect to the relation between the anatomy of the delta and charging/trapping conditions. In order to mature the shallow gas play, a multidisciplinary workflow was applied to the SNS delta that involves 1) the reconstruction of the internally complex delta body, 2) a combined deterministic/stochastic approach to make reservoir property predictions, 3) evaluation of the HC origin, and 4) a grain-size based method to predict the seal-integrity of the sealing clay layers. The results present the first steps towards de-risking the shallow gas play in terms of trapping geometry, seal capacity, sourcing and migration. The presented workflow is applicable to areas were limited exploration data is available, but where critical production data is (still) missing.