Decadal-scale Variability Research Articles

What can be learned about carbon cycle climate feedbacks from the CO<sub>2</sub> airborne fraction?

Abstract. The ratio of CO2 accumulating in the atmosphere to the CO2 flux into the atmosphere due to human activity, the airborne fraction AF, is central to predict changes in earth's surface temperature due to greenhouse gas induced warming. This ratio has remained remarkably constant in the past five decades, but recent studies have reported an apparent increasing trend and interpreted it as an indication for a decrease in the efficiency of the combined sinks by the ocean and terrestrial biosphere. We investigate here whether this interpretation is correct by analyzing the processes that control long-term trends and decadal-scale variations in the AF. To this end, we use simplified linear models for describing the time evolution of an atmospheric CO2 perturbation. We find firstly that the spin-up time of the system for the AF to converge to a constant value is on the order of 200–300 years and differs depending on whether exponentially increasing fossil fuel emissions only or the sum of fossil fuel and land use emissions are used. We find secondly that the primary control on the decadal time-scale variations of the AF is variations in the relative growth rate of the total anthropogenic CO2 emissions. Changes in sink efficiencies tend to leave a smaller imprint. Therefore, before interpreting trends in the AF as an indication of weakening carbon sink efficiency, it is necessary to account for trends and variations in AF stemming from anthropogenic emissions and other extrinsic forcing events, such as volcanic eruptions. Using atmospheric CO2 data and emission estimates for the period 1959 through 2006, and our simple predictive models for the AF, we find that likely omissions in the reported emissions from land use change and extrinsic forcing events are sufficient to explain the observed long-term trend in AF. Therefore, claims for a decreasing long-term trend in the carbon sink efficiency over the last few decades are currently not supported by atmospheric CO2 data and anthropogenic emissions estimates.

Determining lateral migration rates of meandering rivers using fallout radionuclides

We explore the novel technique of using short-lived fallout radionuclides to date fluvial surfaces with the goal of determining lateral migration rates. Specifically, we use the fallout radionuclide 210Pb (half-life t 1/2 ~ 22.3 years) to determine the lateral migration rates of meandering reaches on the Winooski River, VT, the upper Connecticut River, NH, and the Genesee River, NY. We find that, particularly near the channel, 210Pb ex inventories are affected by the initial 210Pb ex inventories of freshly deposited sediment (inheritance). Inheritance differs at each site, with lower inheritance occurring at sites with larger upstream drainage areas. After accounting for inheritance, 210Pb ex inventories in surface sediments along a transect orthogonal to the channel yield migration rates of 0.7, 3.1, and 4.7 m/y for the Winooski, Connecticut, and Genesee Rivers, respectively. These rates agree well with values derived independently from historical aerial photography. Variations in 210Pb ex inventories along the transects also provide details of the channel migration histories not evident from the limited available aerial photographs, including evidence for both nearly constant linear and episodic channel migrations. Results suggest the broad applicability and added value of our approach for quantifying decadal-scale variations in fluvial surface ages.

The sustained observatory over the Porcupine Abyssal Plain (PAP): Insights from time series observations and process studies

Oceanographic research in the past 20 years has highlighted the importance of understanding decadal-scale variation in the oceans in order to predict how the ocean will respond to climate change. Climate factors control many of the processes that regulate the input of nutrients to the euphotic zone, primary productivity, zooplankton responses, the downward flux of organic matter, the biomass and composition of seabed communities and, ultimately, the burial of carbon in deep-sea sediments. A critical part of our understanding of the interdependence of these many elements comes from long-term eulerian observations, such as the Hawaii Ocean Time series (HOT) (Karl et al., 2003), the Bermuda Atlantic Time Series (BATS) (Steinberg et al., 2001), the NE Pacific Station M (Smith and Druffel, 1998) and the NE Atlantic Porcupine Abyssal Plain site (PAP) ([Billett and Rice, 2001] and [Lampitt et al., 2001]). Each time series site is considered as representing a different oceanic setting and each has a different suite of observations and history. However, the unifying theme of them all is to understand the time varying properties and processes of the oceanic environment. Only at Station M and PAP have water column and seabed observations been integrated, a feature of some considerable advantage. This special issue presents the latest work at PAP.

Comparisons of drought variability between central High Asia and monsoonal Asia: Inferred from tree rings

Severe drought is a serious natural disaster that frequently strikes East Asia, highlighting the need to understanding its drought regime and the associations with Asian monsoon. Tree-ring-based drought reconstructions provide invaluable paleoclimatic archives for detecting regional and large-scale drought variability and their potential forcings. We herein reviewed many drought reconstructions from central High Asia and monsoonal Asia and compared their similarities and differences, as well as their linkages to Asia monsoon. We compared the decadal-scale variability of six drought reconstructions for the central High Asia, where differing drought variations were found between the western and eastern portions. Seven drought reconstructions were reviewed for monsoonal Asia, from which a difference in drought variability was observed between the northern and southern parts. Therefore, we compared the drought variations of the four sub-regions of western and eastern parts of central High Asia, as well as northern and southern portions of monsoonal Asia. ENSO activity and sea surface temperature of western Pacific and northern Indian Oceans, coupled with Asian monsoon, play an important role in modulating drought variability of much area of the East Asia. An improved denser multi-index tree-ring network of longer length for East Asia is necessary for the establishment of more reliable large-scale drought reconstruction.

Decadal-scale rainfall variability in Ethiopia recorded in an annually laminated, Holocene-age, stalagmite

An annually laminated, uranium-series dated, Holocene stalagmite from southeast Ethiopia has been analysed for growth rate and δ13C and δ18O variations at annual to biennial resolution, in order to provide the first long duration proxy record of decadal-scale rainfall variability in this climatically sensitive region. Our study site (10°N) is climatically influenced by both summer (June—August) and spring (March—May) rainfall caused by the annual movement of the Inter-Tropical Convergence Zone (ITCZ) and modulated by large-scale anomalies in the atmospheric circulation and in ocean temperatures. Here we show that stalagmite growth, episodic throughout the last 7800 years, demonstrates decadal-scale (8—25 yr) variability in both growth rate and δ 18O. A hydrological model was employed and indicates that this decadal variability is due to variations in the relative amounts of rainfall in the two rain seasons. Our record, unique in its combination of length (a total of ~1000 years), annual chronology and high resolution δ18O, shows for the first time that such decadal-scale variability in rainfall in this region has occurred through the Holocene, which implies persistent decadal-scale variability for the large-scale atmospheric and oceanic driving factors.

A molluscan perspective on hydrological cycle dynamics in northwestern Europe

AbstractShell aragonite δ180 values of unionid freshwater mussels are applied as a proxy for past river discharges in the rivers Rhine and Meuse, using a set of nine shells from selected climatic intervals during the late Holocene. A single Meuse shell derives from the Subboreal and its δ180 values are similar to modern values. The Rhine specimens represent the Subboreal, the Roman Warm Period and the Medieval Warm Period (MWP). These shells also show averages and ranges of aragonite δ180 values similar to modern specimens. This indicates that environmental conditions such as Rhine river dynamics, Alpine meltwater input and drought severity during these intervals were similar to the 20th century. These shells do not record subtle centennial to millennial climatic variation due to their relatively short lifespan and the large inter-annual and intra-seasonal variation in environmental conditions. However, they are very suitable for studying seasonal to decadal scale climate variability. The two shells with the longest lifespan appear to show decadal scale variability in reconstructed water δ180 values during the MWP, possibly forced by the North Atlantic Oscillation (NAO), which is the dominant mode of variability influencing precipitation regimes over Europe.

Linkage of the Boreal Spring Antarctic Oscillation to the West African Summer Monsoon

The relationship between the boreal spring (or the austral autumn) Antarctic Oscillation (AAO) (March– April) and the West African summer monsoon (WASM) (June–September) is analyzed based on NCEP/NCAR reanalysis data. The results show that the linkage of the boreal spring AAO to the WASM exhibits decadal-scale variations: a strong connection between the two appears over the period 1985–2006 and a weak connection over the period 1970–1984. Further analysis indicates that such an unstable relationship between the two results from the modulation by ENSO events to a large extent. A possible mechanism for the impacts of the boreal spring AAO on the WASM is also discussed. The variability of the boreal spring tropical South Atlantic sea surface temperature (SST) appears to serve as a bridge linking these two systems. The boreal spring AAO produces an anomalous SST over the tropical South Atlantic by exciting an equatorward Rossby wave train over the western Southern Hemisphere (SH). This AAO-related SST anomaly modulates the meridional gradient of moist static energy (MSE) between the Sahel and the Guinea-tropical Atlantic region in the boreal spring. The MSE gradient is of paramount importance for the changes from spring to summer in the West African monsoon because its relaxation along the seasonal cycle is linked to the northward excursion of the WASM system into the African continent. Therefore, an anomalous AAO-related MSE gradient can lead to anomalous Sahel rainfall in the early summer. When this rainfall occurs over the Sahel, the local positive soil moisture-rainfall feedback plays a crucial role in sustaining and prolonging this rainfall anomaly throughout the whole summer.

The response of a jack pine forest to late-Holocene climate variability in northwestern Wisconsin

Terrestrial plant communities have the potential to respond to climate change rapidly, if dominant species are killed by a series of extreme events, or slowly, if the cumulative effects of shorter-term climate fluctuations result in long-term compositional change. We used pollen and charcoal records from a lake and a testate amoebae-derived history of water-table depth in a nearby peatland to assess the response of the jack pine-dominated forests of northwestern Wisconsin to the climate variability of the last ~2000 years. The hydrology record and the charcoal record indicate that the climate near Warner Lake over the last ~2000 years was characterized by multidecadal variation in moisture availability with no apparent multicentennial-long trends in moisture balance or fire frequency. However, the pollen record suggests that there were multicentennial-scale changes in the vegetation composition around Warner Lake. Direct comparison of the three proxy records is challenging, because of their differing temporal resolutions and the complexity of potential ecological responses to climate variability. Therefore, we developed an interpretive model to compare multiple simulated proxies under two scenarios of environmental variability in order to determine under what conditions apparently contradictory records are likely to be found. The interpretive model reveals that a record of multicentennial-long change in vegetation is possible if multidecadal climate variability interacts with ecological processes influencing the direction and magnitude of succession. Compositional changes in the Warner Lake pollen record could reflect long-term variation in temperature, seasonality or other climate factors independent of moisture balance; however it is also possible that multidecadal moisture variability interacted with ecological processes affecting recruitment and mortality of species following fires of varying size and severity. Decadal-scale climatic variability can lead to altered successional pathways and to changes in forest composition that last for centuries.

Reconstructed droughts for the southeastern Tibetan Plateau over the past 568 years and its linkages to the Pacific and Atlantic Ocean climate variability

We present a Palmer Drought Severity Index reconstruction (r = 0.61, P < 0.01) from 1440 to 2007 for the southeastern Tibetan Plateau, based on tree rings of the forest fir (Abies forrestii). Persistent decadal dry intervals were found in the 1440s-1460s, 1560s-1580s, 1700s, 1770s, 1810s, 1860s and 1980s, and the extreme wet epochs were the 1480s-1490s, 1510s-1520s, 1590s, 1610s-1630s, 1720s-1730s, 1800s, 1830s, 1870s, 1930s, 1950s and after the 1990s. Comparisons of our record with those identified in other moisture related reconstructions for nearby regions showed that our reconstructed droughts were relatively consistent with those found in other regions of Indochina, suggesting similar drought regimes. Spectral peaks of 2.3-5.5 years may be indicative of ENSO activity, as also suggested by negative correlations with SSTs in the eastern equatorial and southeastern Pacific Ocean. Significant multidecadal spectral peaks of 29.2-40.9 and 56.8-60.2 years were identified. As indicated by the spatial correlation patterns, the decadal-scale variability may be linked to SST variations in the northern Pacific and Atlantic Oceans.

Early 20th century Arctic warming in retrospect

AbstractThe major early 20th century climatic fluctuation (∼1920–1940) has been the subject of scientific enquiry from the time it was detected in the 1920s. The papers of scientists who studied the event first‐hand have faded into obscurity but their insights are relevant today. We review this event through a rediscovery of early research and new assessments of the instrumental record. Much of the inter‐annual to decadal scale variability in surface air temperature (SAT) anomaly patterns and related ecosystem effects in the Arctic and elsewhere can be attributed to the superposition of leading modes of variability in the atmospheric circulation. Meridional circulation patterns were an important factor in the high latitudes of the North Atlantic during the early climatic fluctuation. Sea surface temperature (SST) anomalies that appeared during this period were congruent with low‐frequency variability in the climate system but were themselves most likely the result of anomalous forcing by the atmosphere. The high‐resolution data necessary to verify this hypothesis are lacking, but the consistency of multiple lines of evidence provides strong support. Our findings indicate that early climatic fluctuation is best interpreted as a large but random climate excursion imposed on top of the steadily rising global mean temperature associated with anthropogenic forcing. Copyright © 2009 Royal Meteorological Society

Possible mechanisms of decadal‐scale variation in PO4concentration in the western North Pacific

[1] We suggest possible mechanisms of decadal-scale variation in PO 4 concentration in the Oyashio and Kuroshio-Oyashio transition waters, western North Pacific. Significant decreasing and increasing trends in PO 4 have been observed in the surface and mid-layers of the ocean in this region, respectively. Synchronous bidecadal-scale oscillations in PO 4 were also found between the two layers. Differences in the relationship of the trends and the oscillation in these layers suggest that they are driven by separate processes. The trend component may be induced by attenuation of water exchange between the two layers. In contrast, the influence of the 18.6-yr period nodal tidal cycle on the formation rate of intermediate water in the Okhotsk Sea may cause the bidecadal-scale oscillation. The PO 4 concentration showed a significant positive correlation with Neocalanus plumchrus biomass, the dominant mesozooplankton species in the Oyashio and Kuroshio― Oyashio Transition waters. These relationships suggest that the variation in PO 4 affected production of N. plumchrus due to changes in primary production.

Synchronous multidecadal fish recruitment patterns in Chesapeake Bay, USA

Multispecies fish recruitment patterns within Chesapeake Bay were investigated in four fishery-independent survey data sets (one primary and three ancillary data sets) that together span the years 1968–2004. These independently conducted surveys record interannual recruitment variability for 15 ecologically and economically important fish species of the Northeast US Continental Shelf Large Marine Ecosystem. Principal component analyses revealed that the strongest multispecies recruitment pattern (first principal component) present in each data set describes a negative recruitment relationship between anadromous and coastal shelf-spawning species. Among the data sets, the first principal component accounted for 31%–42% of multispecies variance. Locally weighted regression modeling revealed that the decadal-scale variability accounted for 62% of the variance in the primary data set’s first principal component’s (annual) scores, whereas interannual variability accounted for only 38%. Despite strong differences in sampling methods, sampled habitats, and sampling locations, this pattern of antagonistic recruitment between Chesapeake Bay anadromous and shelf-spawning (CBASS) species was synchronously correlated among data sets at both decadal and interannual scales. The CBASS pattern has tended to persist in one mode for periods lasting longer than a decade and tends to reverse sign rather within only 2–3 years. A statistically significant regime shift occurred in 1992, when recruitment in anadromous fishes became favored at the expense of recruitment of shelf-spawning estuarine-dependant fishes.

Influence of atmospheric teleconnections and Upper Circumpolar Deep Water on phytoplankton biomass around Elephant Island, Antarctica

Using 18 years of hydrographic data collected during austral summer from 1990 to 2007, we examined the association between atmospheric teleconnections, seasonal mean water column properties and phytoplankton biomass around Elephant Island (EI), Antarctica. We developed an index of the extent of Upper Circumpolar Deep Water (UCDW) in the EI region, defined as the mean temperature at the 27.6 kg m -3 (σt) isopycnal. We found a positive correlation (r = 0.60; p < 0.001) between this index of UCDW extent and the magnitude of the seasonal Southern Oscillation Index (SOI). No linear secular trend was observed in temperature at the 27.6 σt isopycnal, but significant interannual patterns of variability were observed and polynomial regression suggested that potential long-term decadal (or longer) scale variability was captured. Mean Upper Mixed Layer (UML) chlorophyll a (chl a) concentration was not correlated with this UCDW index, but was positively cor- related with the strength of the SOI. Mean integrated chl a biomass of the UML was positively corre- lated (r = 0.88; p < 0.001) with the mean UML chl a concentration. Stepwise regression showed that variability in mean UML chl a concentration over the 18-yr time series was more strongly correlated with UML temperature than UML depth. Although the correlations were weak, these results suggest that the deepening of the UML during El Nino conditions was likely the result of colder temperatures within the UML that limited bloom conditions over this 18-yr time series, with the opposite pattern during La Nina.

Paleoecological studies on variability in marine fish populations: A long-term perspective on the impacts of climatic change on marine ecosystems

The use of historical fishing records to understand relationships between climatic change and fish abundance is limited by the relatively short duration of these records, and complications due to the strong influence of human activity in addition to climatic change. Sedimentary records containing scales, bones or geochemical proxies of variability in fish populations provide unique insights on long-term ecosystem dynamics and relationships with climatic change. Available records from Holocene sediments are summarized and synthesized. The records are from several widespread locations near or along the continental margins of the South Atlantic and Pacific oceans, including Alaska, USA (Pacific salmon), Saanich and Effingham Inlets, British Columbia, Canada (pelagic fish), Santa Barbara Basin, California, USA (Northern anchovies and Pacific sardines), Gulf of California, Mexico (Pacific sardines, Northern anchovies and Pacific hake), Peru upwelling system (sardines, anchovies and hake), and Benguela Current System, South Africa (sardines, anchovies and hake). These records demonstrate that fish population sizes are not constant, and varied significantly over a range of time scales prior to the advent of large-scale commercial fishing. In addition to the decadal-scale variability commonly observed in historical records, the long-term records reveal substantial variability over centennial and millennial time scales. Shifts in abundance are often, but not always, correlated with regional and/or global climatic changes. The long-term perspective reveals different patterns of variability in fish populations, as well as fish–climate relationships, than suggested by analysis of historical records. Many records suggest prominent changes in fish abundance at ca. 1000–1200 AD, during the Little Ice Age, and during the transition at the end of the Little Ice Age in the 19th century that may be correlative, and that were likely driven by major hemispheric or global reorganizations in the earth's climate system. Additional sedimentary records of marine fish abundance and corresponding paleoenvironmental conditions are likely to further enhance our understanding of marine ecosystem dynamics.

Is the decadal variability in the tropical Atlantic a precursor to the NAO?

Abstract. In the past two decades climate research in the tropical Atlantic with respect to the inter-hemispheric gradient of sea surface temperature (SST) emphasized the predominance of decadal-scale variability. Our results show that this mode of variability is prevalent only for part of the last 130-years record (the 1880s, the 1920s and, especially, the 1970s). There is a lag of a few months between the decadal variations of the inter-hemispheric gradient of SST and the decadal variability of the North Atlantic Oscillation (NAO). This seems to indicate that the 10-year variability first develops in the tropics and then propagates polewards. The inter-hemispheric gradient of SST mode should be thought as episodic and not as a periodic oscillation.

Decadal-scale variation in dune erosion and accretion rates: An investigation of the significance of changing storm tide frequency and magnitude on the Sefton coast, UK

Monitoring of frontal dune erosion and accretion on the Sefton coast in northwest England over the past 50 years has revealed significant spatial and temporal variations. Previous work has shown that the spatial variations primarily reflect longshore differences in beach and nearshore morphology, energy regime and sediment budget, but the causes of temporal variations have not previously been studied in detail. This paper presents the results of work carried out to test the hypothesis that a major cause of temporal variation is changes in the frequency and magnitude of storms, surges and resulting high tides. Dune toe erosion/accretion records dating from 1958 have been compared with tide gauge records at Liverpool and Heysham. Relatively high dune erosion rates at Formby Point 1958–1968 were associated with a relatively large number of storm tides. Slower erosion at Formby, and relatively rapid accretion in areas to the north and south, occurred during the 1970's and 1980's when there were relatively few major storm tides. After 1990 rates of dune erosion at Formby increased again, and dunes to the north and south experienced slower accretion. During this period high storm tides have been more frequent, and the annual number of hours with water levels above the critical level for dune erosion has increased significantly. An increase in the rate of mean sea-level rise at both Liverpool and Heysham is evident since 1990, but we conclude that this factor is of less importance than the occurrence of extreme high tides and wave action associated with storms. The incidence of extreme high tides shows an identifiable relationship with the lunar nodal tidal cycle, but the evidence indicates that meteorological forcing has also had a significant effect. Storms and surges in the eastern Irish Sea are associated with Atlantic depressions whose direction and rate of movement have a strong influence on wind speeds, wave energy and the height of surge tides. However, preliminary analysis has indicated only a modest relationship between dune erosion/accretion rates and the North Atlantic Oscillation index.

A pressure gradient metric capturing planetary‐scale influences on eastern Australian rainfall

The Gayndah‐Deniliquin index (GDI), a measure of the north‐south atmospheric pressure gradient across eastern Australia, is presented. The 113 year long GDI record reveals strong interannual to decadal scale variability in zonal geostrophic wind flow across eastern Australia. The GDI, as a measure of easterly geostrophic wind strength and associated moisture transport from the Pacific Ocean, is shown to be significantly correlated with summer rainfall over vast areas of the Australian continent, especially over the Murray Darling Basin and the state of New South Wales. The latest abrupt decline in the GDI, which commenced around 2001, corresponded with the onset of a severe prolonged drought across eastern Australia. We demonstrate that the northern and southern poles of the MSLP derived GDI are differentially influenced by El Niño‐Southern Oscillation (ENSO) and the Southern Annular Mode (SAM). Understanding the effects of these interactions between SAM and ENSO on moisture transport to eastern Australia could have implications for future Australian climate variability and climate change.

Recent changes in solar outputs and the global mean surface temperature. III. Analysis of contributions to global mean air surface temperature rise

A multivariate fit to the variation in global mean surface air temperature anomaly over the past half century is presented. The fit procedure allows for the effect of response time on the waveform, amplitude and lag of each radiative forcing input, and each is allowed to have its own time constant. It is shown that the contribution of solar variability to the temperature trend since 1987 is small and downward; the best estimate is −1.3% and the 2 σ confidence level sets the uncertainty range of −0.7 to −1.9%. The result is the same if one quantifies the solar variation using galactic cosmic ray fluxes (for which the analysis can be extended back to 1953) or the most accurate total solar irradiance data composite. The rise in the global mean air surface temperatures is predominantly associated with a linear increase that represents the combined effects of changes in anthropogenic well-mixed greenhouse gases and aerosols, although, in recent decades, there is also a considerable contribution by a relative lack of major volcanic eruptions. The best estimate is that the anthropogenic factors contribute 75% of the rise since 1987, with an uncertainty range (set by the 2 σ confidence level using an AR(1) noise model) of 49–160%; thus, the uncertainty is large, but we can state that at least half of the temperature trend comes from the linear term and that this term could explain the entire rise. The results are consistent with the intergovernmental panel on climate change (IPCC) estimates of the changes in radiative forcing (given for 1961–1995) and are here combined with those estimates to find the response times, equilibrium climate sensitivities and pertinent heat capacities (i.e. the depth into the oceans to which a given radiative forcing variation penetrates) of the quasi-periodic (decadal-scale) input forcing variations. As shown by previous studies, the decadal-scale variations do not penetrate as deeply into the oceans as the longer term drifts and have shorter response times. Hence, conclusions about the response to century-scale forcing changes (and hence the associated equilibrium climate sensitivity and the temperature rise commitment) cannot be made from studies of the response to shorter period forcing changes.

CLIMATE OF THE ARCTIC MARINE ENVIRONMENT

The climate of the Arctic marine environment is characterized by strong seasonality in the incoming solar radiation and by tremendous spatial variations arising from a variety of surface types, including open ocean, sea ice, large islands, and proximity to major landmasses. Interannual and decadal-scale variations are prominent features of Arctic climate, complicating the distinction between natural and anthropogenically driven variations. Nevertheless, climate models consistently indicate that the Arctic is the most climatically sensitive region of the Northern Hemisphere, especially near the sea ice margins. The Arctic marine environment has shown changes over the past several decades, and these changes are part of a broader global warming that exceeds the range of natural variability over the past 1000 years. Record minima of sea ice coverage during the past few summers and increased melt from Greenland have important implications for the hydrographic regime of the Arctic marine environment. The recent changes in the atmosphere (temperature, precipitation, pressure), sea ice, and ocean appear to be a coordinated response to systematic variations of the large-scale atmospheric circulation, superimposed on a general warming that is likely associated with increasing greenhouse gases. The changes have been sufficiently large in some sectors (e.g., the Bering/Chukchi Seas) that consequences for marine ecosystems appear to be underway. Global climate models indicate an additional warming of several degrees Celsius in much of the Arctic marine environment by 2050. However, the warming is seasonal (largest in autumn and winter), spatially variable, and closely associated with further retreat of sea ice. Additional changes predicted for 2050 are a general decrease of sea level pressure (largest in the Bering sector) and an increase of precipitation. While predictions of changes in storminess cannot be made with confidence, the predicted reduction of sea ice cover will almost certainly lead to increased oceanic mixing, ocean wave generation, and coastal flooding.

Interannual hypoxia variability in a coastal upwelling system: Ocean–shelf exchange, climate and ecosystem-state implications

In this study we use multi-year time series to examine the dynamic characteristics of coupled physical–biogeochemical processes that modulate interannual coastal hypoxia in the Benguela upwelling system in the southeast Atlantic. The results confirmed earlier findings on the role of advection to explain much of the seasonal–decadal variability. These results challenge the predominantly biogeochemical basis, namely benthic–pelagic coupling, to understand the variability of hypoxia and its ecosystem implications. Unexpectedly, the results showed that the variability was insensitive to changes in the electron-donating capacity (carbon export fluxes) but strongly dependent on the advected oxygen fluxes. The dynamics of the interaction of equatorial and polar boundary conditions (ocean–shelf exchange) and seasonally phased shelf advection were the key forcing functions that explained hypoxia variability in seasonal–decadal time scales. The vulnerability of the system to climate change lies in the long-term response of the equatorial system that governs seasonal and interannual warming at the Angola–Benguela front as well as wind stress in the Luderitz southern boundary that governs ventilation. The proposed model was able to explain most of the decadal scale variability of two different ecosystem-state indicators. The model predicts a long-term decline of present ecosystem function with climate change.