Initial Warming Research Articles

Improvement of the heat treatment of Jack pine (Pinus banksiana) using ThermoWood technology

Thermal treatment in inert atmosphere is used to preserve wood without utilisation of toxic chemical agents. In addition, this process increases the dimensional stability of the wood matrix and results in attractive dark colour. On the other hand, it can deteriorate the mechanical strength and the flexibility of wood. For this reason, heat treatment parameters (such as maximum temperature, heating rate, the duration of the first plateau at constant temperature (100–120°C) and the second plateau at the maximum treatment temperature, humidity, final cool down rate) must be optimised in order to benefit from advantages of thermal treatment without deteriorating significantly the mechanical properties of wood. Correlation between wood properties and thermal treatment parameters depends not only on the wood species but also the environment (climate, soil) where the given species grow. This paper presents a study on thermal treatment of Canadian Jack pine (Pinus banksiana) using a medium size prototype furnace. The aim of this study was to optimize the set of parameters used during industrial treatments. The possibility of shortening the process time without causing any deterioration in wood quality was also investigated. The results show that increasing the maximum heat-treatment temperature increased the dimensional stability of Jack pine and darkened its colour. This parameter did not affect the modulus of elasticity but it decreased the modulus of rupture of Jack pine. A slight reduction in gas humidity during the initial warming up period permitted to shorten the drying period and at the same time increased the mechanical strength. This improvement helps save energy and increase productivity.

THE PALEOCENE-EOCENE THERMAL MAXIMUM: NEW DATA ON MICROFOSSIL TURNOVER AT THE ZUMAIA SECTION, SPAIN

The benthic foraminiferal turnover and extinction event (BEE) associated with the negative carbon isotope excursion (CIE) across the Paleocene–Eocene Thermal Maximum (PETM) is analyzed in the Zumaia section (Spain), one of the most complete and expanded deep-water sequences known worldwide. New biostratigraphic, paleoecologic, and paleoenvironmental data on benthic foraminifera are correlated to information on planktic foraminiferal and calcareous nannofossil turnover in order to evaluate possible causes and consequences of the PETM. Gradual but rapid extinction of 18% of the benthic foraminiferal species starts at the onset of the CIE, after the initial ocean warming (as inferred from calcareous nannofossils) recorded in the last 46 kyr of the Paleocene. This gradual extinction event culminated ∼10.5 kyr after the onset of the CIE and led to the main BEE, affecting 37% of the species. Therefore, extinctions across the PETM affected a total of 55% of the benthic foraminiferal species at Zumaia. The gradual extinction occurred under inferred oxic conditions without evidence for carbonate dissolution, indicating that carbonate corrosivity and oxygenation of the ocean bottom waters were not the main cause of the event. An interval characterized by dissolution occurs above the main BEE, suggesting that bottom waters became corrosive after the main extinction. Carbonate is progressively better preserved through the overlying deposits, and carbon isotope values gradually return to background levels. These data are consistent with a slow deepening of the carbonate compensation depth after its initial rise owing to abrupt acidification of the oceans. Microfossil data support a rapid onset of the PETM, followed by long-term effects on calcareous plankton and benthic foraminifera.

A Matter of Humidity

The water vapor feedback is the process whereby an initial warming of the planet, caused, for example, by an increase in atmospheric carbon dioxide, leads to an increase in the humidity of the atmosphere. Because water vapor is itself a greenhouse gas, this increase in humidity causes additional warming. The water vapor feedback has long been expected to strongly amplify climate changes because of the expectation that the atmosphere’s relative humidity would remain roughly constant— meaning that the specific humidity would increase at the rate of the equilibrium vapor pressure, which rises rapidly with temperature. However, observational evidence has been harder to come by, and the effect has been controversial. Much of that controversy can now be laid to rest, thanks to new observations and better theoretical understanding.

Centennial‐scale evolution of Dansgaard‐Oeschger events in the northeast Atlantic Ocean between 39.5 and 56.5 ka B.P.

There is much uncertainty surrounding the mechanisms that forced the abrupt climate fluctuations found in many palaeoclimate records during Marine Isotope Stage (MIS)‐3. One of the processes thought to be involved in these events is the Atlantic Meridional Overturning Circulation (MOC), which exhibited large changes in its dominant mode throughout the last glacial period. Giant piston core MD95‐2006 from the northeast Atlantic Ocean records a suite of palaeoceanographic proxies related to the activity of both surface and deep water masses through a period of MIS‐3 when abrupt climate fluctuations were extremely pronounced. A two‐stage progression of surface water warming during interstadial warm events is proposed, with initial warming related to the northward advection of a thin warm surface layer within the North Atlantic Current, which only extended into deeper surface layers as the interstadial progressed. Benthic foraminifera isotope data also show millennial‐scale oscillations but of a different structure to the abrupt surface water changes. These changes are argued to partly be related to the influence of low‐salinity deepwater brines. The influence of deepwater brines over the site of MD95‐2006 reached a maximum at times of rapid warming of surface waters. This observation supports the suggestion that brine formation may have helped to destabilize the accumulation of warm, saline surface waters at low latitudes, helping to force the MOC into a warm mode of operation. The contribution of deepwater brines relative to other mechanisms proposed to alter the state of the MOC needs to be examined further in future studies.

Another Side to the Climate-Cloud Conundrum Finally Revealed

GLOBAL WARMING Clouds have always given climate modelers fits. The clouds in their models are crude at best, and in the real world, researchers struggle to understand how clouds are responding to—and perhaps magnifying—greenhouse warming. As a result, cloud behavior is the biggest single source of uncertainty in climate prediction. But two new studies now show that much of the worry about clouds' role in the warming has been misdirected. Clouds' response to global temperature changes may be much quicker and more direct—and thus easier to study—than experts have thought. “It's a little bit of good news,” says climate researcher Brian Soden of the University of Miami in Florida. “People have been working on [the cloud problem] for 2 decades or more, and we haven't done a lot to decrease the uncertainty. I'm a little more optimistic now about making progress on this problem.” Researchers have always considered the cloud problem a matter of feedbacks. In a positive feedback, increasing greenhouse gases warm the surface, and the warmer surface then feeds back somehow to overlying clouds. The nature of the feedback remains mysterious, but if it's positive, it would decrease global cloud cover. With fewer clouds reflecting solar energy back into space, more energy would reach Earth, amplifying the initial warming. But Earth's surface and especially its oceans are slow to warm, so cloud feedbacks operate over decades—or so scientists assumed. Two groups have recently looked at just how quickly model clouds actually respond to an increase in greenhouse gases. Climate researchers Jonathan Gregory and Mark Webb, both of the Hadley Centre for Climate Prediction and Research in Exeter, U.K., report in the January Journal of Climate (issue 1) that model clouds, at least, can respond quickly to added carbon dioxide—in months, not decades. In most of the models examined, the classic cloud feedback driven by change at the surface played only a minor role. The real action took place where the clouds themselves were, up in the air. Added carbon dioxide absorbs more long-wave energy radiating from the surface; the air holding that carbon dioxide warms, and clouds evaporate, letting more solar radiation in. ![Figure][1] At risk. Greenhouse gases can directly reduce cloud cover and magnify warming. CREDIT: UCAR In follow-up work in press in Geophysical Research Letters , climate researchers Timothy Andrews and Piers Forster, both of the University of Leeds, U.K., extend and refine the analysis of Gregory and Webb. In seven models, they doubled carbon dioxide while holding the global surface temperature constant and watched how atmospheric temperatures respond. The classic, slow cloud response is only half of previous estimates, they find, and most of the cloud response is fast. Scientists “have been looking at the incorrect part of the problem,” says Forster. Properly accounting for fast response is important when modeling rising temperatures under the strengthening greenhouse, Webb and Gregory argue. And because it is fast and therefore has been going on for decades, notes Gregory, researchers may be able to tease the newly appreciated cloud response out of observations and improve their models faster than they have the past few decades. [1]: pending:yes

Late Cenozoic climate changes in China's western interior: a review of research on Lake Qinghai and comparison with other records

We review Late Cenozoic climate and environment changes in the western interior of China with an emphasis on lacustrine records from Lake Qinghai. Widespread deposition of red clay in the marginal basins of the Tibetan Plateau indicates that the Asian monsoon system was initially established by ∼8 Ma, when the plateau reached a threshold altitude. Subsequent strengthening of the winter monsoon, along with the establishment of the Northern Hemisphere ice sheets, reflects a long-term trend of global cooling. The few cores from the Tibetan Plateau that reach back a million years suggest that they record the mid-Pleistocene transition from glacial cycles dominated by 41 ka cycles to those dominated by 100 ka cycles. During Terminations I and II, strengthening of the summer monsoon in China's interior was delayed compared with sea level and insolation records, and it did not reach the western Tibetan Plateau and the Tarim Basin. Lacustrine carbonate δ 18O records reveal no climatic anomaly during MIS3, so that high terraces interpreted as evidence for extremely high lake levels during MIS3 remain an enigma. Following the Last Glacial Maximum (LSM), several lines of evidence from Lake Qinghai and elsewhere point to an initial warming of regional climate about 14 500 cal yr BP, which was followed by a brief cold reversal, possibly corresponding to the Younger Dryas event in the North Atlantic region. Maximum warming occurred about 10 000 cal yr BP, accompanied by increased monsoon precipitation in the eastern Tibetan Plateau. Superimposed on this general pattern are small-amplitude, centennial-scale oscillations during the Holocene. Warmer than present climate conditions terminated about 4000 cal yr BP. Progressive lowering of the water level in Lake Qinghai during the last half century is mainly a result of negative precipitation–evaporation balance within the context of global warming.

Termination of Indian Ocean Dipole Events in a Coupled General Circulation Model

Abstract Using 200 yr of coupled general circulation model (CGCM) results, causes for the termination of Indian Ocean dipole (IOD) events are investigated. The CGCM used here is the Scale Interaction Experiment-Frontier Research Center for Global Change (SINTEX-F1) model, which consists of a version of the European Community–Hamburg (ECHAM4.6) atmospheric model and a version of the Ocean Parallelise (OPA8.2) ocean general circulation model. This model reproduces reasonably well the present-day climatology and interannual signals of the Indian and Pacific Oceans. The main characteristics of the intraseasonal disturbances (ISDs)/oscillations are also fairly well captured by this model. However, the eastward propagation of ISDs in the model is relatively fast in the Indian Ocean and stationary in the Pacific compared to observations. A sudden reversal of equatorial zonal winds is observed, as a result of significant intraseasonal disturbances in the equatorial Indian Ocean in November–December of IOD events, which evolve independently of ENSO. A majority of these IOD events (15 out of 18) are terminated mainly because of the 20–40-day ISD activity in the equatorial zonal winds. Ocean heat budget analysis in the upper 50 m clearly shows that the initial warming after the peak of the IOD phenomenon is triggered by increased solar radiation owing to clear-sky conditions in the eastern Indian Ocean. Subsequently, the equatorial jets excited by the ISD deepen the thermocline in the southeastern equatorial Indian Ocean. This deepening of the thermocline inhibits the vertical entrainment of cool waters and therefore the IOD is terminated. IOD events that co-occur with ENSO are terminated owing to anomalous incoming solar radiation as a result of prevailing cloud-free skies. Further warming occurs seasonally through the vertical convergence of heat due to a monsoonal wind reversal along Sumatra–Java. On occasion, strong ISD activities in July–August terminated short-lived IOD events by triggering downwelling intraseasonal equatorial Kelvin waves.

Modulation of the bipolar seesaw in the Southeast Pacific during Termination 1

The termination of the last ice age (Termination 1; T1) is crucial for our understanding of global climate change and for the validation of climate models. There are still a number of open questions regarding for example the exact timing and the mechanisms involved in the initiation of deglaciation and the subsequent interhemispheric pattern of the warming. Our study is based on a well-dated and high-resolution alkenone-based sea surface temperature (SST) record from the SE-Pacific off southern Chile (Ocean Drilling Project Site 1233) showing that deglacial warming at the northern margin of the Antarctic Circumpolar Current system (ACC) began shortly after 19,000 years BP (19 kyr BP). The timing is largely consistent with Antarctic ice-core records but the initial warming in the SE-Pacific is more abrupt suggesting a direct and immediate response to the slowdown of the Atlantic thermohaline circulation through the bipolar seesaw mechanism. This response requires a rapid transfer of the Atlantic signal to the SE-Pacific without involving the thermal inertia of the Southern Ocean that may contribute to the substantially more gradual deglacial temperature rise seen in Antarctic ice-cores. A very plausible mechanism for this rapid transfer is a seesaw-induced change of the coupled ocean–atmosphere system of the ACC and the southern westerly wind belt. In addition, modelling results suggest that insolation changes and the deglacial CO 2 rise induced a substantial SST increase at our site location but with a gradual warming structure. The similarity of the two-step rise in our proxy SSTs and CO 2 over T1 strongly demands for a forcing mechanism influencing both, temperature and CO 2. As SSTs at our coring site are particularly sensitive to latitudinal shifts of the ACC/southern westerly wind belt system, we conclude that such latitudinal shifts may substantially affect the upwelling of deepwater masses in the Southern Ocean and thus the release of CO 2 to the atmosphere as suggested by the conceptual model of [Toggweiler, J.R., Rusell, J.L., Carson, S.R., 2006. Midlatitude westerlies, atmospheric CO 2, and climate change during ice ages. Paleoceanography 21. doi:10.1029/2005PA001154].

Tribute to R. G. Boutilier: Skin colour and body temperature changes in baskingBokermannohyla alvarengai(Bokermann 1956)

In amphibians solar basking far from water sources is relatively uncommon since the highly permeable amphibian skin does not represent a significant barrier to the accompanying risk of losing water by evaporation. A South American frog, Bokermannohyla alvarengai (Bokermann 1956), however, spends a significant amount of the day exposed to full sun and relatively high temperatures. The means by which this frog copes with potentially high rates of evaporative water loss and high body temperatures are unknown. Thus, in this study, skin colour changes, body surface temperature, and evaporative water loss rates were examined under a mixture of field and laboratory conditions to ascertain whether changes in skin reflectivity play an important role in this animal's thermal and hydric balance. Field data demonstrated a tight correlation between the lightness of skin colour and frog temperature, with lighter frogs being captured possessing higher body temperatures. Laboratory experiments supported this relationship, revealing that frogs kept in the dark or at lower temperatures (20 degrees C) had darker skin colours, whereas frogs kept in the light or higher temperatures (30 degrees C) had skin colours of a lighter hue. Light exhibited a stronger influence on skin colour than temperature alone, suggesting that colour change is triggered by the increase in incident solar energy and in anticipation of changes in body temperature. This conclusion is corroborated by the observation that cold, darkly coloured frogs placed in the sun rapidly became lighter in colour during the initial warming up period (over the first 5 min), after which they warmed up more slowly and underwent a further, albeit slower, lightening of skin colour. Surprisingly, despite its natural disposition to bask in the sun, this species does not possess a ;waterproof' skin, since its rates of evaporative water loss were not dissimilar from many hylid species that live in arboreal or semi-aquatic environments. The natural history of B. alvarengai is largely unknown and, therefore, it is likely that the herein reported colour change and basking behaviour represent a complex interaction between thermoregulation and water balance with other ecologically relevant functions, such as crypsis.

Abatement of Greenhouse Gases: Does Location Matter?

Today's climate policy is based on the assumption that the location of emissions reductions has no impact on the overall climate effect. However, this may not be the case since reductions of greenhouse gases generally will lead to changes in emissions of short-lived gases and aerosols. Abatement measures may be primarily targeted at reducing CO2, but may also simultaneously reduce emissions of NOx, CO, CH4 and SO2 and aerosols. Emissions of these species may cause significant additional radiative forcing. We have used a global 3-D chemical transport model and a radiative transfer model to study the impact on climate in terms of radiative forcing for a realistic change in location of the emissions from large-scale sources. Based on an assumed 10% reduction in CO2 emissions, reductions in the emissions of other species have been estimated. Climate impact for the SRES A1B scenario is compared to two reduction cases, with the main focus on a case with emission reductions between 2010 and 2030, but also a case with sustained emission reductions. The emission reductions are applied to four different regions (Europe, China, South Asia, and South America). In terms of integrated radiative forcing (over 100 yr), the total effect (including only the direct effect of aerosols) is always smaller than for CO2 alone. Large variations between the regions are found (53–86% of the CO2 effect). Inclusion of the indirect effects of sulphate aerosols reduces the net effect of measures towards zero. The global temperature responses, calculated with a simple energy balance model, show an initial additional warming of different magnitude between the regions followed by a more uniform reduction in the warming later. A major part of the regional differences can be attributed to differences related to aerosols, while ozone and changes in methane lifetime make relatively small contributions. Emission reductions in a different sector (e.g. transportation instead of large-scale sources) might change this conclusion since the NOx to SO2 ratio in the emissions is significantly higher for transportation than for large-scale sources. The total climate effect of abatement measures thus depends on (i) which gases and aerosols are affected by the measure, (ii) the lifetime of the measure implemented, (iii) time horizon over which the effects are considered, and (iv) the chemical, physical and meteorological conditions in the region. There are important policy implications of the results. Equal effects of a measure cannot be assumed if the measure is implemented in a different region and if several gases are affected. Thus, the design of emission reduction measures should be considered thoroughly before implementation.

Characterisation of cryoinjury in Euglena gracilis using flow-cytometry and cryomicroscopy

Flow-cytometry and cryomicroscopy elucidated that the unicellular algal protist Euglena gracilis was undamaged by cryoprotectant added at 0 °C, and super-cooling in the absence of ice. Cryoinjuries were however induced by: osmotic shock resulting from excessive cryodehydration, intracellular ice, and fracturing of the frozen medium on thawing. Suboptimal cooling at −0.3 °C min −1 to −60 °C and osmotic shock invariably resulted in damage to the organism’s pellicle and osmoregulatory system causing, a significant ( P > 0.005) increase in cell size. Cell damage was not repairable and led to death. The responses of E. gracilis to cryopreservation as visualised by flow-cytometry and cryomicroscopy assisted the development of an improved storage protocol. This comprised: cryoprotection with methanol [10%(v/v)] at 0 °C, cooling at 0.5 °C min −1 to −60 °C, isothermal hold for 30 min, and direct immersion in liquid nitrogen. Highest post-thaw viability (>60%) was obtained using two-step thawing, which involved initial slow warming to −130 °C followed by relatively rapid warming (∼90 °C min −1) to ambient temperature (ca. 25 °C).

Dynamical greenhouse-plus feedback and polar warming amplification. Part I: A dry radiative-transportive climate model

In this paper, we use a dry radiative-transportive climate model to illustrate that the atmospheric poleward heat transport plays an important role in amplifying the polar surface warming due to anthropogenic greenhouse gases. Because of a much warmer surface in tropics, the anthropogenic radiative forcing is larger in tropics than in extratropics for same amount of anthropogenic greenhouse gases. A direct response to the anthropogenic radiative forcing is an increase in the atmosphere equator-to-pole temperature contrast, leading to a strengthening of the atmospheric poleward heat transport. As a result, part of the extra amount of energy intercepted by the low-latitude atmosphere due to an increase in its opacity is transported to high latitudes. This implies a “greenhouse-plus” (“greenhouse-minus”) feedback to the high (low) latitude surface temperatures, which acts to amplify (reduce) the initial surface warming in high (low) latitudes and may cause a larger surface warming in high latitudes. The Stefan–Boltzmann feedback suppresses the negative dynamical feedback in low latitudes more strongly than the positive in high latitudes, amplifying the global mean surface temperature warming. Because of the oceanic poleward heat transport, the ocean surface temperature in extratropics is warmer in winter compared to the land, implying a larger radiative forcing for the same amount of anthropogenic greenhouse gases. The same dynamical feedback mechanism would also amplify the land surface warming in extratropics by transporting part of the extra amount of energy intercepted by the atmosphere over the ocean surface to land. This explains partly why the observed land surface warming in extratropics is stronger than the surrounding oceans in winter.

Recovery of thermohaline circulation under CO 2 stabilization and overshoot scenarios

In this study we examine the behavior of the thermohaline circulation, as simulated by the Community Climate System Model version 3 (CCSM3), for several centuries following CO 2 stabilization for the SRES B1 and A1B scenarios and for an “overshoot” scenario in which CO 2 levels temporarily reach the same level as in the A1B scenario before declining to an ultimate stabilization level that is identical to the B1 case. While we find no evidence for irreversible changes of the thermohaline circulation in the overshoot experiment, the interplay of the different timescales of the temperature response of the surface and interior ocean does lead to a number of differences in the long-term response of the ocean between it and the B1 stabilization scenario where the same GHG levels are approached by different paths. The stronger initial warming and its slow penetration into the deeper ocean, followed by a transient surface cooling in the overshoot scenario leads to lower static stability, deeper mixing, and a more rapid recovery of the thermohaline circulation than in the B1 stabilization scenario. While the overshoot scenario recovers surface conditions (e.g. SST, sea ice extent) very similar to the B1 scenario shortly after reaching the same GHG levels, the additional accumulation of heat in the interior ocean during the period of higher forcing causes the global mean ocean temperature and steric sea level to remain higher than in the B1 stabilization scenario for at least another several centuries.

Late glacial and Holocene vegetation and regional climate variability evidenced in high-resolution pollen records from Lake Baikal

High-resolution pollen records from Lake Baikal revealed considerable regional differences in the vegetation development and pronounced climate variability during the last glacial–interglacial transition and Holocene. Correlation between cores was successfully based on a chronology constructed from AMS 14C dating of pollen concentrates. Comparison to other radiocarbon-dated pollen sequences from the Baikal region suggests that the chronology presented is very reliable, and thus correlation to other dated events can easily be performed. Pollen indices, which reflect relative changes in major vegetation types and limitations of growing conditions by moisture availability and temperature, demonstrate near-synchronous vegetation changes, which suggest synchronous large-scale climate variation across the Baikal region. Due to the limited influence of human impact in the Lake Baikal region, the pollen data illustrate that, in the continental interior of NE Eurasia Holocene, climate variability was very pronounced. After initial warming and a strong increase in relative moisture (ca. 16 cal ka BP), the Bølling–Allerød-like event was punctuated by three cool and dry events. These events, dated between ca. 15 and 13 cal ka BP, can be compared to coolings as recorded in GISP 2 oxygen isotope records from Greenland ice cores. An expansion of Betula sect. Nanae/ Fruticosae, Artemisia and Chenopodiaceae marks the Younger-Dryas (YD)-like cooling event (ca. 12.5–12 cal ka BP). High temperatures and favourable moisture conditions during the first part of Holocene favoured the optimum development of dark coniferous taiga between 11–7.5 cal ka BP in the south and 10–8 cal ka BP in the northeast. A fir and spruce decline in the southern mountains (ca. 9.5–8.5 cal ka BP) can be related to the 8.2 cal ka BP cooling event. The pronounced mid-Holocene cooling event and a transition towards dry conditions (ca. 8–7 cal ka BP) preceded the nearly synchronous regional expansion of pine taiga. Maximum distribution of Scots pine forests marks the Holocene thermal optimum (ca. 6.5–5.7 cal ka BP), which was followed by two subsequent cooling events (ca. 5.5–4.5 cal ka BP) at the Atlantic–Subboreal transition. A subsequent temperature optimum in the southeastern Baikal region ended with pronounced cooling during the Subboreal–Subatlantic transition (ca. 3–2.5 cal ka BP). A late spread of shrub alders may evidence the beginning of the Little Ice Age.

Holocene North Atlantic surface circulation and climatic variability: evidence from diatom records

Diatom analyses have been performed on a 425cm long Holocene marine sediment sequence from the North Atlantic south of Iceland and a 920cm sediment core spanning the last c. 7500 years from Skalafjord, Faeroe Islands. Additional core data include stable isotopes and results from magnetic susceptibility measurements, while chronostratigraphic control has been provided by AMS 14C measurements. The diatom records reveal distinct changes in North Atlantic surface circulation and climate that have been correlated with published terrestrial and marine records. Initial Holocene warming is dated at 9900 14C years BP, and after a Preboreal cold spell enhanced North Atlantic Current activity and warming prevailed from 9600 to 8800 14C years BP. From 8800 to 8000 "4C years BP the advection of warm Atlantic water masses weakened, presumably under atmospheric circulation conditions characterized by a dominating negative NAO. Prior to the Holocene Climatic Optimum (6000-5000 14C years BP) distinct hydrographic gradients existed in the northern North Atlantic that were probably most pronounced during the reported '8200 cal. years BP cold event'. After 5000 "4C years BP both core records indicate increased climate instability and periods of cooling ('Neoglaciation'), with enhanced cyclone activity affecting the northern North Atlantic particularly at around 4700, 4200, 3200, 2000, 1500 and 1000 14C years BP.

Release of methane from a volcanic basin as a mechanism for initial Eocene global warming.

A 200,000-yr interval of extreme global warming marked the start of the Eocene epoch about 55 million years ago. Negative carbon- and oxygen-isotope excursions in marine and terrestrial sediments show that this event was linked to a massive and rapid (approximately 10,000 yr) input of isotopically depleted carbon. It has been suggested previously that extensive melting of gas hydrates buried in marine sediments may represent the carbon source and has caused the global climate change. Large-scale hydrate melting, however, requires a hitherto unknown triggering mechanism. Here we present evidence for the presence of thousands of hydrothermal vent complexes identified on seismic reflection profiles from the Vøring and Møre basins in the Norwegian Sea. We propose that intrusion of voluminous mantle-derived melts in carbon-rich sedimentary strata in the northeast Atlantic may have caused an explosive release of methane--transported to the ocean or atmosphere through the vent complexes--close to the Palaeocene/Eocene boundary. Similar volcanic and metamorphic processes may explain climate events associated with other large igneous provinces such as the Siberian Traps (approximately 250 million years ago) and the Karoo Igneous Province (approximately 183 million years ago).

Were there two Borrobol Tephras during the early Lateglacial period: implications for tephrochronology?

A series of AMS radiocarbon measurements of terrestrial plant macrofossil remains are presented from a lake sequence in southernmost Sweden in an attempt to constrain the age of the Borrobol Tephra. This recently identified ash layer has been frequently suggested as a potentially significant marker horizon for assessing the precise timing of the initial warming in different parts of Europe at the start of Greenland Interstadial 1 (GI-1). Two different methods are adopted in order to derive a calendar age estimate for this event. An age of ca 13,900 Cariaco varve yrs BP is derived from a visual wiggle match of the age series to the Cariaco Basin data-set. The second approach is based on Bayesian probability analysis and constrains the age of the Borrobol Tephra in southern Sweden to between 13,800–14,450 and 13,667–14,331 cal yrs BP (95% confidence), using the Cariaco and Lake Suigetsu records as calibration data-sets, respectively. These new age-depth models, together with the pollen stratigraphy, suggest that the Borrobol Tephra as found in southern Sweden falls within the late Older Dryas/GI-1d or the early Allerød/GI-1c, whereas other European sequences indicate that this tephra falls close to the GS-2/GI-1 transition. Whether or not this indicates that the different occurrences of the BT in northern Europe are coeval is discussed and the implications that arise for the application of tephrochronology during this period are outlined.

Temperature Influences Nitrogen Release Rates in Cranberry Soils

Native nitrogen is released when soils are mineralized. The amount of N released by this process depends on the amount of organic matter present and soil temperature. Cranberry (Vaccinium macrocarpon Ait.) grows in acidic soils with a wide range in organic matter content. To evaluate release of cranberry soil N at varied soil temperatures, intact soils were collected from sites that had received no fertilizer. Soils were cored and placed in polyvinyl chloride (PVC) columns 20 cm deep × 5 cm in diameter. Four different soil types, representing the array of conditions in cranberry soil (mineral, sanded organic, organic peat, and muck) were used. Additional columns of sand soil (pH 4.5) that had been pH adjusted to high (6.5) and low (3.0) were also prepared. Each column was incubated sequentially at six different temperatures from 10 to 24 °C (2.8 °C temperature intervals) for 3 weeks at each temperature, with the soils leached twice weekly to determine the amount of N release. The total amount of N in leachate was highest in the organic soils, intermediate in the sanded organic, and lowest in the sands. At the lowest temperature (10 °C), higher amounts of N were released in sanded organic and sand than in organic soils. This was attributed to a flush of mineralization with change in the aerobic status and initial soil warming. The degree of decomposition in the organic soils was important in determining which form of N predominated in the leachate. In the more highly decomposed soil (muck), most of the N was converted to nitrate. In the pH adjusted sand, high soil pH (6.5) resulted in an increase in nitrate in the leachate but no change in ammonium when compared to non-adjusted (pH 4.5) and acidified (pH 3.0) treatments. This study suggests that for cranberry soils with organic matter content of at least 1.5% little to no soil-applied fertilizer N is needed early in the season, until soil temperatures reach 13 °C. This temperature is consistent with the beginning of active nutrient uptake by roots. Soil N release from native organic matter was fairly consistent until soil temperatures exceeded 21 °C, indicating that when temperatures exceed 21 °C, planned fertilizer applications should be reduced, particularly in highly organic soils.

Decadal-scale variations of water mass properties in the deep Weddell Sea

Data from cruises between 1989 and 2003 with FS Polarstern were used to construct section-wide potential temperature and salinity time series of the main water masses in the Weddell Gyre. In tandem with these CTD data, two time series between 1989 and 1995 are presented from moored instruments in the central Weddell Sea. The regional and methodological consistency of the dataset allows us to quantify variations which are not visible in less homogeneous datasets. The data reveal significant temperature and salinity variations of the Warm Deep Water and the Weddell Sea Bottom Water on a decadal time scale. The longest time series were obtained at the prime meridian. Here warming is observed in the Warm Deep Water from 1992 to 1998 followed by cooling. In the Weddell Sea proper, measurements of instruments moored in the Weddell Sea Bottom Water layer recorded a temperature increase over 6 years at a rate of 0.01 °C a−1. After the mooring period, CTD casts in 1998 point to a weakening of the trend. The warming trend in the bottom water occurs over most of the Weddell Sea, as detected in the additional CTD surveys. The variations are close to the detection level in the voluminous Weddell Sea Deep Water. The initial warming trend of the Warm Deep Water is consistent with warming trends reported in literature of subsurface waters of the Antarctic Circumpolar Current. The reversal of the trend in the Weddell Sea seems to be related to variations of the atmospheric conditions which can affect both the intrusion of Circumpolar Deep Water from the north and the circulation of the Weddell Gyre. Because the Warm Deep Water is the major source water for the formation of deep and bottom water in the Weddell Sea, it is suggested that its increase in temperature and salinity is likely to at least partly cause the variations which were observed in the bottom water.

Extending the limits of the Borrobol Tephra to Scandinavia and detection of new early Holocene tephras

Analyses of two infilled lakes in Blekinge, southeast Sweden, indicate the presence of at least three tephra horizons of Termination 1 and early Holocene age. Geochemical analyses confirm the presence of the Borrobol Tephra, the Askja Tephra (10,000 14C yr B.P.), and one previously unreported tephra of Icelandic origin. Extending the limits of the Borrobol Tephra to Scandinavia illustrates that this ash is far more widespread than previously realized and is therefore, an important marker horizon for determining the rate and timing of the initial warming at the start of Greenland Interstade 1 (GI-1) within Europe. The relatively unknown Askja Tephra and the newly discovered Hässeldalen Tephra are stratigraphically placed at the Younger Dryas/Preboreal transition. This paper demonstrates the suitability and success associated with the extraction techniques for tracing microtephra horizons in areas distal to volcanic sources.