Decadal Climate Variability Research Articles

Recent Shift in the Warming of the Southern Oceans Modulated by Decadal Climate Variability

AbstractIt has been reported that the Southern Hemisphere oceans experienced rapid warming during the decade‐long global surface warming slowdown (2003–2012) and the earlier period of the Argo record (2006–2013). In this study, we analyze updated observations to show that this rapid warming has slowed down, leading to less contribution of the Southern Hemisphere oceans to the global ocean heat storage (∼65% over the available Argo period 2006–2019). Two warming hotspot regions, the southeast Indian Ocean and South Pacific Ocean, have experienced cooling over 2013–2019. This decadal shift is related to variations in the Southern Annular Mode and Interdecadal Pacific Oscillation. The isopycnal deepening (shoaling) forced by changing winds dominated the regional ocean temperature changes over the earlier warming (later cooling) period. Our finding demonstrates how decadal variability modulates long‐term climate change and provides important observational information for the ongoing calibration of decadal prediction systems.

A Global, Multiproduct Analysis of Coastal Marine Heatwaves: Distribution, Characteristics, and Long‐Term Trends

AbstractMajor marine heatwave (MHW) events have caused catastrophic impacts on coastal marine ecosystems. However, to date there has not been a global assessment of MHWs in coastal areas where rich marine ecosystems are at risk. Here, we combine four satellite Sea Surface Temperature (SST) products to quantify the distribution, characteristics, and decadal trend of coastal MHWs, using an ensemble approach. Hotspots of MHW stress, defined as yearly cumulative intensity, were found to be concentrated in mid latitude coasts like the Mediterranean Sea, Japan Sea, and Tasman Sea, as well as the north‐eastern coast of the United States. We found a global increase in coastal MHW frequency and duration during the past 25 years by 1–2 events per decade and 5–10 days per decade, respectively, with regional distribution closely related to decadal climate variability. Increases in frequency and duration of MHWs has led to large increases of cumulative intensity and yearly cumulative intensity, particularly in mid‐latitudes and hotspot regions. Long‐term changes in mean SST were the main driver of the observed trends of coastal MHWs, while internal variability was important for explaining local decreases in MHW metrics such as along the south‐eastern Pacific coast. MHW average metrics and trends were consistent across all four products used in this analysis, giving high confidence in the results. However, important differences between products were observed for MHW mean intensity, which was well correlated to SST variability, suggesting sensitivity of this metric to the specific SST data set and demonstrating a need for an ensemble approach to MHW analysis.

The relative roles of decadal climate variations and changes in the ocean observing system on seasonal prediction skill of tropical Pacific SST

In this study, we examined the temporal variations of the El Nino-Southern Oscillation (ENSO) prediction skill during 1958–2016 in the context of the evolution in the tropical Pacific subsurface ocean observing system. To examine the temporal variations of the seasonal prediction skill, spatial correlation skill (SCS) of the predicted SST anomalies (SSTA) in the tropical Pacific Ocean within 10oS-10oN and temporal correlation skill (TCS) of the area-averaged SSTA throughout the same basin for the four periods of 1958–1978, 1979–1994, 1995–2005 and 2006–2016 were evaluated. These periods correspond to low amount, first increase, medium amount and second increase of the subsurface ocean temperature observations. Our results show that the influence of the observing system is detectable in the skill increase—both in SCS and TCS metrics—during the period 1995–2005. However, the impact of the subsurface ocean observing system is difficult to quantify in the prediction skill metrics during 2006–2016. It is shown that SCS is determined to a large extent by the magnitude of the observed SSTA in the target month. There is visible skill increase in the TCS before and after 1979, but this appears to be the result of variations in the properties of the verifying SST. Thus, potential impacts of the observing system are masked by climate variations of SST at decadal time scales, which may be real or result of variations in the SST observing system. In particular, the multidecadal modulations of the tropical Pacific SST associated with the climate shifts in the late 1970s and the early 2000s have more significant influence on prediction skill than the changes in observing system.

El Niño Southern Oscillation and decadal climate variability impacts on crop yields and adaptation value

Abstract Ocean-atmospheric phenomena (OAP) have been found to be associated with regional climate variability and, in turn, agricultural production. Previous research has shown that advance information on OAP and its climate implications could provide valuable opportunities to adjust agriculture practices. In this study, we review OAP effects on crop yields, covering both shorter-term El Niño Southern Oscillation (ENSO) and longer-term ocean-related decadal climate variability (DCV) phenomena, such as Pacific Decadal Oscillation (PDO), the Tropical Atlantic Gradient (TAG), and the West Pacific Warm Pool (WPWP). We review both statistical approaches and simulation models that have been used to assess OAP impacts on crop yields. Findings show heterogeneous impacts across crops, regions, OAP phases, and seasons. Evidence also indicates that more frequent and extreme OAP phases would damage agriculture. However, economic gains could be achieved via adaptation strategies responding to the early release of OAP phase information. Discussions on current knowledge gaps and future research issues are included.

Decadal climate variability, water availability and cropping: the value of forecast information in South-Central Texas

Decadal climate variability (DCV) phenomena are ocean-based conditions that have climate influences persisting for a decade or more. Few studies have addressed the coupled agricultural and economic implications of these phenomena. Here, we investigate the economic value of DCV information in a South Central Texas case study along with the nature of possible adaptations to the information. To do this we first perform an econometric estimation of DCV impacts on regional crop yields and groundwater recharge. We then expand a regional economic and hydrological model to include DCV information. We find significant DCV impacts on regional aquifer recharge and crop yields for oats, dryland sorghum, and irrigated winter wheat. DCV information has substantial value with perfect information ranging from US$3.79-3.93 million yr-1 plus benefits for springflow protection, while a less perfect forecast is worth $1.47-1.89 million yr-1. We also find DCV adaptations involve changes in crop mix and water use.

Exploring North Atlantic and North Pacific Decadal Climate Prediction Using Self-Organizing Maps

AbstractDecadal climate prediction can provide invaluable information for decisions made by government agencies and industry. Modes of internal variability of the ocean play an important role in determining the climate on decadal time scales. This study explores the possibility of using self-organizing maps (SOMs) to identify decadal climate variability, measure theoretical decadal predictability, and conduct decadal predictions of internal climate variability within a long control simulation. SOM is applied to an 11-yr running-mean winter sea surface temperature (SST) in the North Pacific and North Atlantic Oceans within the Community Earth System Model 1850 preindustrial simulation to identify patterns of internal variability in SSTs. Transition probability tables are calculated to identify preferred paths through the SOM with time. Results show both persistence and preferred evolutions of SST depending on the initial SST pattern. This method also provides a measure of the predictability of these SST patterns, with the North Atlantic being predictable at longer lead times than the North Pacific. In addition, decadal SST predictions using persistence, a first-order Markov chain, and lagged transition probabilities are conducted. The lagged transition probability predictions have a reemergence of prediction skill around lag 15 for both domains. Although the prediction skill is very low, it does imply that the SOM has the ability to predict some aspects of the internal variability of the system beyond 10 years.

Coarse sediment dynamics in a large glaciated river system: Holocene history and storage dynamics dictate contemporary climate sensitivity

Abstract The gravel-bedded White River drains a 1279 km2 basin in Washington State, with lowlands sculpted by continental glaciation and headwaters on an actively glaciated stratovolcano. Chronic aggradation along an alluvial fan near the river’s mouth has progressively reduced flood conveyance. In order to better understand how forecasted climate change may influence coarse sediment delivery and aggradation rates in this lowland depositional setting, we assessed the contemporary delivery and routing of coarse sediment through the watershed; this assessment was based on a rich set of topographic, sedimentologic, and hydrologic data from the past century, with a focus on repeat high-resolution topographic surveys from the past decade. We found that most of the lower river’s contemporary bed-load flux originates from persistent erosion of alluvial deposits in the lower watershed. This erosion is a response to a drop in local base level caused by a major avulsion across the fan in 1906 and then augmented by subsequent dredging. The 1906 avulsion and modern disequilibrium valley profiles reflect landscape conditioning by continental glaciation and a massive mid-Holocene lahar. In the proglacial headwaters, infrequent large sediment pulses have accomplished most of the observed coarse sediment export, with exported material blanketing downstream valley floors; during typical floods, transported bed material is largely sourced from erosion of these valley floor floods. Throughout the watershed, we observe decadal-scale coarse sediment dynamics strongly related to the filling or emptying of valley-scale sediment storage over 102–104 yr time scales, often in response to major disturbances that either emplace large deposits or influence their redistribution. Paraglacial responses in large watersheds are suggested to be inherently complicated and punctuated as a result of internal landform interactions and stochastic/threshold-dependent events. We argue that, in combination, Holocene disturbance, storage dynamics, and human flow modification make coarse sediment fluxes in the lower White River relatively insensitive to decadal climate variability. Results highlight the degree to which river sensitivity to contemporary disturbance, climatic or otherwise, may be contingent on local and idiosyncratic watershed histories, underscoring the need to unpack those histories while demonstrating the utility of watershed-scale high-resolution topography toward that end.

North Atlantic climate far more predictable than models imply.

Quantifying signals and uncertainties in climate models is essential for the detection, attribution, prediction and projection of climate change1-3. Although inter-model agreement is high for large-scale temperature signals, dynamical changes in atmospheric circulation are very uncertain4. This leads to low confidence in regional projections, especially for precipitation, over the coming decades5,6. The chaotic nature of the climate system7-9 may also mean that signal uncertainties are largely irreducible. However, climate projections are difficult to verify until further observations become available. Here we assess retrospective climate model predictions of the past six decades and show that decadal variations in North Atlantic winter climate are highly predictable, despite a lack of agreement between individual model simulations and the poor predictive ability of raw model outputs. Crucially, current models underestimate the predictable signal (the predictable fraction of the total variability) of the North Atlantic Oscillation (the leading mode of variability in North Atlantic atmospheric circulation) by an order of magnitude. Consequently, compared to perfect models, 100 times as many ensemble members are needed in current models to extract this signal, and its effects on the climate are underestimated relative to other factors. To address these limitations, we implement a two-stage post-processing technique. We first adjust the variance of the ensemble-mean North Atlantic Oscillation forecast to match the observed variance of the predictable signal. We then select and use only the ensemble members with a North Atlantic Oscillation sufficiently close to the variance-adjusted ensemble-mean forecast North Atlantic Oscillation. This approach greatly improves decadal predictions of winter climate for Europe and eastern North America. Predictions of Atlantic multidecadal variability are also improved, suggesting that the North Atlantic Oscillation is not driven solely by Atlantic multidecadal variability. Our results highlight the need to understand why the signal-to-noise ratio is too small in current climate models10, and the extent to which correcting this model error would reduce uncertainties in regional climate change projections on timescales beyond a decade.

Effects of the Pacific Decadal Oscillation on Thailand monsoon rainfall derived from a 194-year tree ring width chronology of teak trees from northwestern Thailand.

Thailand is a predominantly agricultural country. An understanding of the dominant driver of decadal-scale changes in Thailand monsoon (TM) rainfall trends is particularly important in terms of agro-meteorological information and monsoon predictions. In this study, a 194-year tree ring chronology of teak trees in northwestern Thailand was developed. Correlations between the tree ring width index (i.e., the Susa index) and climate variables confirmed that this index can be used as a proxy for rainfall in the early monsoon season from May to July. Similar variations with other regional tree ring chronologies confirmed the reliability of the climate signals embedded in the tree ring widths. The possible relationship between the Susa index-based TM rainfall and the Pacific Decadal Oscillation (PDO) was examined. Spectral analysis showed statistically significant PDO periodicities of between 22 and 24years. The spatial correlations detected across the key regions of the PDO revealed associations with the north Pacific sea surface temperature during recent decades. The long-term relationships between the Susa index and the PDO were nonstationary at the decadal timescale. Positive correlations were found for AD 1824-1875 and AD 1900-1955, whereas negative relationships prevailed for AD 1876-1899 and 1956-2017. The El Niño Southern Oscillation-related anomalous TM was indeed stronger during both the warm and cold phases of the PDO. The PDO is therefore identified as a driving factor of decadal climate variability. This study leads the way to understanding the changes in the TM-PDO relationship over time and demonstrates the utility of teak tree ring width as a potential proxy for PDO teleconnection.

Decadal variability of tropical Indian Ocean sea surface temperature and its impact on the Indian summer monsoon

Decadal variability of climate over the Pacific and Atlantic Ocean is well studied. However, the decadal climate variability over the Indian Ocean and its possible impact on the summer monsoon received relatively less attention. The present study aims to explore the decadal variability of the Tropical Indian Ocean (TIO) sea surface temperature (SST) and its associations with the Indian summer monsoon rainfall (ISMR) variability. More than a hundred years of observed monthly SST data from Extended Reconstructed sea surface temperature and rainfall data from India Meteorological Department are used for the analysis. In addition to these, century reanalysis fields of winds, moisture, vertical velocity, tropospheric temperature, and sea level pressure are used for diagnosing different processes. Time series and wavelet analysis confirmed the presence of decadal variability (~ 9 to 30 years) in the TIO SST. The decadal variance of TIO SST is maximum in the eastern equatorial Indian Ocean, followed by the north Arabian Sea. Decadal EOF of TIO SST shows a dominant basin-wide mode explaining about 50% of total variance and has robust decadal variability during 1940 to 1952; wavelet analysis supported this robust signal statistically. Similar analysis for the ISMR reveals that the decadal variance of rainfall has significant strength over monsoon core zone and Western Ghats. The EOF analysis further confirms this spatial pattern of rainfall decadal variability over India. Correlation between of decadal TIO SST and over monsoon core zone (MCZ) rainfall is significant with 2 years lag. To understand how the decadal variability of TIO SST influences the ISMR, monsoon features during strong warm and cold phase are studied. During the warm phase, MCZ and Western Ghats receive more rain than normal and vice versa for cold phase. Which is consistent with strong southwesterly winds, strong pressure gradient, and strong convergence over the MCZ for the warm phase. Also, during the warm phase, positive anomaly of mid-troposphere temperature, vertical velocity, and moist static energy are found to be associated with excess convective activity. Apart from this, larger scale zonal (Walker) and meridional (Hadley) circulation fields are also in phase with the TIO SST and rainfall variability. Our study advocates that decadal variability in TIO SST influences the monsoon dynamics and moist thermodynamics leading to near in-phase changes in the rainfall over the MCZ and Western Ghats region.

The Value of Ocean Decadal Climate Variability Information to United States Agriculture

Ocean-related decadal climate variability (ODCV) has the potential to influence regional climates and, in turn, crop yields. ODCV event forecasts with associated climate and crop yield implication information can provide farmers with the opportunity to alter their crop mixes and input usage to adapt to the forecast conditions. We investigate the value of ODCV information and the nature of adaptations. This is done by estimating the changes in welfare under differing information scenarios using a nonlinear dynamic optimization model. We find evidence that both perfect forecasts and the use of forecasts permitting a conditional probability of future phase combinations can significantly increase agriculture consumer and producer welfare. This is a new result that is an estimate of the US national value of releasing ODCV forecasts and accompanying yield information.

Aquatic community structure as sentinel of recent environmental changes unraveled from lake sedimentary records from the Atacama Desert, Chile.

The Atacama Desert (21–26°S) is currently one of the driest places on Earth and metal(loid)s are of special concern for this region, which hosts the largest-known porphyry copper deposits produced in Chile. Evidence of past environmental conditions is commonly preserved in natural archives, such as lacustrine sediments. Sediment records obtained from Inca Coya Lake (22°20’S-68°35’W, 2534 m.a.s.l.), a small lake located in the Atacama Desert, reflected the evolution of regional mining activity during the 20th century and sedimentation associated with decadal climate variability. We studied the aquatic community structure changes recorded in sediment records from Inca Coya Lake. By analysis of magnetic properties (susceptibility, hysteresis curves and Curie temperatures), grain size and geochemical composition of the sediments, we identified environmental periods and changes in the community of benthic and planktonic organisms (diatoms and diapausing egg bank). We identified three detrital episodes that we interpret as dry/wet phases during the last 90 years associated with the increase of flash flood events promoting hypoxia oscillations; anthropogenic (mining activity) signals were also identified. Invertebrate community structure (primary consumers) reflected the metal exposure, measured as changes in assemblage composition through species turnover. Diatom community composition was best associated with variables related to wetter/drier alternation and consequent changes in oxygen availability. Bioindicators analyzed (diatoms, diapausing egg bank and invertebrate community) demonstrated to be excellent indicators of the bioavailability of compounds in the aquatic ecosystem of Inca Coya Lake, allowing the environmental impact assessment of the water resources due to flash floods and mining activity in the driest desert of the world.

North Pacific subtropical mode water is controlled by the Atlantic Multidecadal Variability

North Pacific subtropical mode water, a vertically homogeneous thermocline water mass, occupies the entire subtropical Western Pacific Ocean. It transports mass, heat and nutrients from the surface to the subsurface ocean, providing memory of climate variability1–11. Decadal variability of the mode water temperature has been attributed to the Pacific Decadal Oscillation (PDO)2,3,12,13, but this is based on short data records. Here, using long records of observations, we show that decadal-to-multidecadal variability of the mode water mean temperature is instead controlled by the Atlantic Multidecadal Variability (AMV). During an AMV-positive phase, warm sea surface temperatures (SSTs) in the North Atlantic Ocean weaken the subtropical North Pacific westerlies; the associated anomalous easterlies in the subtropical west Pacific4,5 drive a northward Ekman transport of warm water to the mode water formation area. Subduction of the warm water increases mode water temperature, influencing Northwestern Pacific upper ocean heat content and fish catches. A long pre-industrial model simulation with multiple AMV cycles and a pacemaker experiment support this mechanism—the AMV forcing alone can drive decadal variability of the mode water. Thus, the AMV provides important memory for prediction of decadal climate and ecosystem variability in the Pacific Ocean. North Pacific mode water controls extratropical-to-tropical heat and mass exchange. Analysis and model simulations show that decadal temperature variations in this subtropical North West Pacific water mass are forced remotely by Atlantic Multidecadal Variability.

Using CESM-RESFire to understand climate–fire–ecosystem interactions and the implications for decadal climate variability

Abstract. Large wildfires exert strong disturbance on regional and global climate systems and ecosystems by perturbing radiative forcing as well as the carbon and water balance between the atmosphere and land surface, while short- and long-term variations in fire weather, terrestrial ecosystems, and human activity modulate fire intensity and reshape fire regimes. The complex climate–fire–ecosystem interactions were not fully integrated in previous climate model studies, and the resulting effects on the projections of future climate change are not well understood. Here we use the fully interactive REgion-Specific ecosystem feedback Fire model (RESFire) that was developed in the Community Earth System Model (CESM) to investigate these interactions and their impacts on climate systems and fire activity. We designed two sets of decadal simulations using CESM-RESFire for present-day (2001–2010) and future (2051–2060) scenarios, respectively, and conducted a series of sensitivity experiments to assess the effects of individual feedback pathways among climate, fire, and ecosystems. Our implementation of RESFire, which includes online land–atmosphere coupling of fire emissions and fire-induced land cover change (LCC), reproduces the observed aerosol optical depth (AOD) from space-based Moderate Resolution Imaging Spectroradiometer (MODIS) satellite products and ground-based AErosol RObotic NETwork (AERONET) data; it agrees well with carbon budget benchmarks from previous studies. We estimate the global averaged net radiative effect of both fire aerosols and fire-induced LCC at -0.59±0.52 W m−2, which is dominated by fire aerosol–cloud interactions (-0.82±0.19 W m−2), in the present-day scenario under climatological conditions of the 2000s. The fire-related net cooling effect increases by ∼170 % to -1.60±0.27 W m−2 in the 2050s under the conditions of the Representative Concentration Pathway 4.5 (RCP4.5) scenario. Such considerably enhanced radiative effect is attributed to the largely increased global burned area (+19 %) and fire carbon emissions (+100 %) from the 2000s to the 2050s driven by climate change. The net ecosystem exchange (NEE) of carbon between the land and atmosphere components in the simulations increases by 33 % accordingly, implying that biomass burning is an increasing carbon source at short-term timescales in the future. High-latitude regions with prevalent peatlands would be more vulnerable to increased fire threats due to climate change, and the increase in fire aerosols could counter the projected decrease in anthropogenic aerosols due to air pollution control policies in many regions. We also evaluate two distinct feedback mechanisms that are associated with fire aerosols and fire-induced LCC, respectively. On a global scale, the first mechanism imposes positive feedbacks to fire activity through enhanced droughts with suppressed precipitation by fire aerosol–cloud interactions, while the second one manifests as negative feedbacks due to reduced fuel loads by fire consumption and post-fire tree mortality and recovery processes. These two feedback pathways with opposite effects compete at regional to global scales and increase the complexity of climate–fire–ecosystem interactions and their climatic impacts.

Decadal variability in twentieth-century ocean acidification in the California Current Ecosystem

Oceanic uptake of CO2 can mitigate climate change, but also results in global ocean acidification. Ocean acidification-related changes to the marine carbonate system can disturb ecosystems and hinder calcification by some organisms. Here, we use the calcification response of planktonic foraminifera as a tool to reconstruct the progression of ocean acidification in the California Current Ecosystem through the twentieth century. Measurements of nearly 2,000 fossil foraminifera shell weights and areas preserved in a marine sediment core showed a 20% reduction in calcification by a surface-dwelling foraminifera species. Using modern calibrations, this response translates to an estimated 35% reduction in carbonate ion concentration, a biologically important chemical component of the carbonate system. Assuming other aspects of the carbonate system, this represents a 0.21 decline in pH, exceeding the estimated global average decline by more than a factor of two. Our proxy record also shows considerable variability that is significantly correlated with Pacific Decadal Oscillation and decadal-scale changes in upwelling strength, a relationship that until now has been obscured by the relatively short observational record. This modulation suggests that climatic variations will play an important role in amplifying or alleviating the anthropogenic signal and progression of ocean acidification in this region. Ocean acidification in the California Current Ecosystem was twice the global average during the past century and influenced by decadal climate variations, according to a record of the calcification rate of planktonic foraminifera from the Santa Barbara Basin.

Warming reduces predictability

Effective decadal climate prediction is urgently needed, but achieving this is still very challenging. Now research suggests that greenhouse warming may compound these difficulties with less predictable global decadal climate variability.

Climate changes and variability in the Great Artesian Basin (Australia), future projections, and implications for groundwater management

The Great Artesian Basin (GAB) in Australia is one of the largest aquifer systems in the world and it supports a range of agriculture, industry, fragile ecosystems, and townships. Climate variability and future projections of climate change will impact on both recharge of the GAB and demands on the resource. Understanding the climate in the GAB region is therefore critical to informing regional groundwater management. Observed decadal climatic variability and trends were assessed for significance with Kendall’s test and investigated in light of future climate scenarios with 40 global climate model (GCM) outputs. Historic climate observations show that the GAB region had become warmer and wetter over the last five to six decades. The annual rainfall increased by 0.95 mm/year2 during the period 1960–2016, although this trend magnitude was neither statistically significant nor uniform geographically across the GAB. The annual means of daily mean, maximum, and minimum temperatures increased during that period by 0.019, 0.019, and 0.020 °C/year, with statistically significant increases in 92.4, 91.4 and 85.1% of the GAB, respectively. Trends of other rainfall statistics associated with recharge indicated an increase of the 95th percentile daily rainfall amount, an increase of average rainfall intensity, and a statistically significant decrease in mean wet-spell length. In contrast with past warm and wet climate, the future climate in the GAB region is projected to be warmer and drier, which would potentially produce serious challenges for groundwater resources management for the region.

Salt Sinking in the Upper South Pacific Subtropical Gyre From 2004 to 2016

AbstractThe salinity in the 50–300‐m water column of the South Pacific subtropical gyre (10°S–30°S) increased from 2004 to 2016. The observed changes are primarily associated with changes in the South Pacific Tropical Water (SPTW) volume, which increased at a rate of (3.17 ± 0.25) 1014 m3 per decade in the region of 10–30°S and 150°E–90°W. The increases in the SPTW volume are caused by increased SPTW production, which increased at a rate of 3.45 ± 2.65 Sv per decade. The temporal variability in the mixed layer accounts for 75 ± 32% of the observed increase in SPTW production. The increases in temporal changes in the mixed layer are due to a deeper mixed layer depth (MLD) in austral winter and a shallower MLD in austral spring. The possible drivers of MLD changes at the air‐sea surface are examined. Among the wind stress curl, buoyancy fluxes, and the turbulence induced by wind stress, changes in the surface buoyancy fluxes play the most important role in the deepening of the MLD during austral winter, and changes in the wind stress play a leading role in the shoaling of the MLD during austral spring. Changes in the buoyancy fluxes during winter and changes in the wind stress in spring can be attributed to increases in the Southern Annular Mode from 2004 to 2016. This study highlights the strong modulation of SPTW formation by decadal climate variability over the subtropical South Pacific.

Temporal variability in foraminiferal morphology and geochemistry at the West Antarctic Peninsula: a sediment trap study

Abstract. The West Antarctic Peninsula (WAP) exhibits strong spatial and temporal oceanographic variability, resulting in highly heterogeneous biological productivity. Calcifying organisms that live in the waters off the WAP respond to temporal and spatial variations in ocean temperature and chemistry. These marine calcifiers are potentially threatened by regional climate change with waters already naturally close to carbonate undersaturation. Future projections of carbonate production in the Southern Ocean are challenging due to the lack of historical data collection and complex, decadal climate variability. Here we present a 6-year-long record of the shell fluxes, morphology and stable isotope variability of the polar planktic foraminifera Neogloboquadrina pachyderma (sensu stricto) from near Palmer Station, Antarctica. This species is fundamental to Southern Ocean planktic carbonate production as it is one of the very few planktic foraminifer species adapted to the marine polar environments. We use these new data to obtain insights into its ecology and to derive a robust assessment of the response of this polar species to environmental change. Morphology and stable isotope composition reveal the presence of different growth stages within this tightly defined species. Inter- and intra-annual variability of foraminiferal flux and size is evident and driven by a combination of environmental forcing parameters, most importantly food availability, temperature and sea ice duration and extent. Foraminiferal growth occurs throughout the austral year and is influenced by environmental change, a large portion of which is driven by the Southern Annular Mode and El Niño–Southern Oscillation. A distinct seasonal production is observed, with the highest shell fluxes during the warmest and most productive months of the year. The sensitivity of calcifying foraminifera to environmental variability in this region, from weeks to decades, has implications both for their response to future climatic change and for their use as palaeoclimate indicators. A longer ice-free season could increase carbonate production in this region at least while carbonate saturation is still high enough to allow for thick tests to grow.

South Pacific Decadal Climate Variability and Potential Predictability

Abstract The South Pacific decadal oscillation (SPDO) characterizes the Southern Hemisphere contribution to the Pacific-wide interdecadal Pacific oscillation (IPO) and is analogous to the Pacific decadal oscillation (PDO) centered in the North Pacific. In this study, upper ocean variability and potential predictability of the SPDO is examined in HadISST data and an atmosphere-forced ocean general circulation model. The potential predictability of the IPO-related variability is investigated in terms of both the fractional contribution made by the decadal component in the South, tropical and North Pacific Oceans and in terms of a doubly integrated first-order autoregressive (AR1) model. Despite explaining a smaller fraction of the total variance, we find larger potential predictability of the SPDO relative to the PDO. We identify distinct local drivers in the western subtropical South Pacific, where nonlinear baroclinic Rossby wave–topographic interactions act to low-pass filter decadal variability. In particular, we show that the Kermadec Ridge in the southwest Pacific enhances the decadal signature more prominently than anywhere else in the Pacific basin. Applying the doubly integrated AR1 model, we demonstrate that variability associated with the Pacific–South American pattern is a critically important atmospheric driver of the SPDO via a reddening process analogous to the relationship between the Aleutian low and PDO in the North Pacific—albeit that the relationship in the South Pacific appears to be even stronger. Our results point to the largely unrecognized importance of South Pacific processes as a key source of decadal variability and predictability.