Richard Matear

The Commonwealth Scientific and Industrial Research Organisation | CSIRO · Oceans and Atmosphere

Between June 2019 and March 2020, thousands of wildfires spread devastation across Australia at the tragic cost of many lives, vast areas of burnt forest, and estimated economic losses upward of AU$100 billion. Exceptionally hot and dry weather conditions, and preceding years of severe drought across Australia, contributed to the severity of the wi...

Ice algae play a fundamental role in shaping sea-ice-associated ecosystems and biogeochemistry. This role can be investigated by field observations; however the influence of ice algae at the regional and global scales remains unclear due to limited spatial and temporal coverage of observations and because ice algae are typically not included in cur...

Droughts and climate-change-driven warming are leading to more frequent and intense wildfires arguably contributing to the severe 2019–2020 Australian wildfires. The environmental and ecological impacts of the fires include loss of habitats and the emission of substantial amounts of atmospheric aerosols. Aerosol emissions from wildfires can lead to...

Assessments of climate forecast skill depend on choices made by the assessor. In this perspective, we use forecasts of the El Niño-Southern-Oscillation to outline the impact of bias-correction on skill. Many assessments of skill from hindcasts (past forecasts) are probably overestimates of attainable forecast skill because the hindcasts are informe...

We detail the system design, model configuration and data assimilation evaluation for the CSIRO Climate retrospective Analysis and Forecast Ensemble system: version 1. CAFE60v1 has been designed with the intention of simultaneously generating both initial conditions for multi-year climate forecasts and a large ensemble retrospective analysis of the...

The CSIRO Climate retrospective Analysis and Forecast Ensemble system: version 1 (CAFE60v1) provides a large (96 member) ensemble retrospective analysis of the global climate system from 1960 to present with sufficiently many realizations and at spatio-temporal resolutions suitable to enable probabilistic climate studies. Using a variant of the ens...

Ice algae play a fundamental role in shaping polar marine ecosystems and biogeochemistry. This role can be investigated by field observations, however the influence of ice algae at the regional and global scales remains unclear due to limited spatial and temporal coverage of observations, and because ice algae are typically not included in current...

Climate-driven trends in ocean temperature and primary productivity are projected to differ greatly across the globe, triggering variable levels of concern for marine biota and ecosystems. Quantifying these changes, and the complex ways in which resource-dependent communities will need to respond, is inherently difficult. Existing uncertainty about...

Ocean colour data are commonly used to quantify primary production, study phytoplankton dynamics and calibrate marine models, thus understanding the origin of errors in the retrieved chlorophyll-a (Chl-a) product is critical. One source of uncertainty in retrieved Chl-a products can be related to large photosynthetic cells, characterised by lower m...

We diagnose changes in the decadal‐mean ocean transport over the 21st century as simulated by the ACCESS‐1.3 model under RCP8.5 forcing. A matrix formulation of advection‐diffusion is used to quantify transport into the ocean interior and from the interior back to the surface. We compute the ocean volumes last ventilated at the surface, as well as...

Global climate models project the intensification of marine heatwaves in coming decades due to global warming. However, the spatial resolution of these models is inadequate to resolve mesoscale processes that dominate variability in boundary current regions where societal and economic impacts of marine heatwaves are substantial. Here we compare the...

Remotely-sensed ocean colour is the main tool for estimating chlorophyll a (Chl-a) concentration and primary productivity on the global scale. In order to investigate the source of errors in remotely-sensed Chl-a concentration we obtained in situ bio-optical properties, in situ reflectances, satellite-derived reflectances and the Chl-a concentratio...

Ocean temperature extreme events such as marine heatwaves are expected to intensify in coming decades due to anthropogenic global warming. Reported ecological and economic impacts of marine heatwaves include coral bleaching, local extinction of mangrove and kelp forests, and elevated mortalities of invertebrates, fishes, seabirds, and marine mammal...

Recent studies have shown that, regardless of model configuration, skill, in terms of target month and forecast lead-time, in predicting El Niño Southern Oscillation (ENSO) remains largely dependent on the temporal characteristics of the boreal spring predictability barrier. Continuing the study by O’Kane et al. (2019), we compare multi-year ensemb...

The tropical Pacific Ocean is a globally significant region of climate‐driven biogeochemical variability. Satellite ocean color algorithms have been used for over 20 years, providing a substantial historical record of global ocean chlorophyll‐a variability. Current chlorophyll algorithms perform better in the tropical Pacific than for the globe. Ne...

We assess the representation of multi-day temperature and rainfall extremes in southeast Australia in three coupled general circulation models (GCMs) of varying resolution. We evaluate the statistics of the modelled extremes in terms of their frequency, duration and magnitude compared to observations, and the model representation of the mid-troposp...

Ocean thermal expansion is a large contributor to observed sea-level rise which is expected to continue into the future. However, large uncertainties exist in sea-level projections among climate models, partially due to inter-model differences in ocean heat uptake and redistribution of buoyancy. Here, the mechanisms of vertical ocean heat and salt...

Roughly a third (~30 ppm) of the carbon dioxide (CO2) that entered the ocean during ice ages is attributed to biological mechanisms. A leading hypothesis for the biological drawdown of CO2 is iron (Fe) fertilisation of the high latitudes, but modelling efforts attribute at most 10 ppm to this mechanism, leaving ~20 ppm unexplained. We show that an...

Recent increases in the frequency of extreme climate events (ECEs) such as heatwaves and floods have been attributed to climate change, and could have pronounced ecosystem and evolutionary impacts because they provide little opportunity for organisms to acclimate or adapt. Here we synthesize information on a series of ECEs in Australia from 2011 to...

The isotopes of carbon (δ13C) and nitrogen (δ15N) are commonly used proxies for understanding the ocean. When used in tandem, they provide powerful insight into physical and biogeochemical processes. Here, we detail the implementation of δ13C and δ15N in the ocean component of an Earth system model. We evaluate our simulated δ13C and δ15N against c...

A method to construct transport matrices from standard ocean-model output, such as mean volume fluxes and mixed-layer depths, is presented. These transport matrices enable highly efficient calculation of deep-water tracer fields that otherwise require long integrations with forward time-stepping ocean models. Comparisons of matrix solutions for ide...

Historical harvesting pushed many whale species to the brink of extinction. Although most Southern Hemisphere populations are slowly recovering, the influence of future climate change on their recovery remains unknown. We investigate the impacts of two anthropogenic pressures—historical commercial whaling and future climate change—on populations of...

The isotopes of carbon (δ¹³C) and nitrogen (δ¹⁵N) are commonly used proxies for understanding the ocean. When used in tandem, they provide powerful insight into physical and biogeochemical processes. Here, we detail the implementation of δ¹³C and δ¹⁵N in the ocean component of an Earth system model. We evaluate our simulated δ¹³C and δ¹⁵N against c...

We develop and compare variants of coupled data assimilation (DA) systems based on ensemble optimal interpolation (EnOI) and ensemble transform Kalman filter (ETKF) methods. The assimilation system is first tested on a small paradigm model of the coupled tropical-extratropical climate system, then implemented for a coupled general circulation model...

Antarctic sea ice trends have to date been linked to surface winds, through sea ice motion and atmospheric thermal advection. This paper analyzes sea ice volume in 10 Coupled Model Intercomparison Project Phase 5 (CMIP5) model configurations under pre-industrial and historical climate forcings, to compare the relative importance of ice motion and t...

Southern Ocean (SO) nutrient export via mode and intermediate waters is known to affect global biological production. The accompanying effects on the CO2 flux outside the SO are less certain. We performed idealized model simulations to separate the transient effects of SO carbon pumps on nutrients, primary production, and CO2 flux outside the SO. T...

The early part of the last deglaciation is characterised by a ~40 ppm atmospheric CO2 rise occurring in two abrupt phases. The underlying mechanisms driving these increases remain a subject of intense debate. Here, we successfully reproduce changes in CO2, δ13C and Δ14C as recorded by paleo-records during Heinrich stadial 1 (HS1). We show that HS1...

We use a global ocean model to investigate the role of dinitrogen (N2) fixation within the global carbon (C) cycle. We find that: 1. N 2 fixation is ~25% (800 Pg C) of the biological C store under preindustrial conditions. 2. The biological C pump is severely limited without N 2 fixers in its capacity to respond to increases in aeolian iron (Fe)...

Atmospheric carbon dioxide (CO2) levels continue to rise, increasing the risk of severe impacts on the Earth system, and on the ecosystem services that it provides. Artificial ocean alkalinization (AOA) is capable of reducing atmospheric CO2 concentrations and surface warming and addressing ocean acidification. Here, we simulate global and regional...

Carbon–climate feedbacks have the potential to significantly impact the future climate by altering atmospheric CO2 concentrations (Zaehle et al. 2010). By modifying the future atmospheric CO2 concentrations, the carbon–climate feedbacks will also influence the future ocean acidification trajectory. Here, we use the CO2 emissions scenarios from fou...

Chlorophyll-a measurements in the form of in situ observations and satellite ocean colour products are commonly used in data assimilation to calibrate marine biogeochemical models. Here, a two size-class phytoplankton biogeochemical model, with a 0D configuration, was used to simulate the surface chlorophyll-a dynamics (simulated surface Chl-a) for...

The biogeochemistry of the ocean exerts a strong influence on the climate by modulating atmospheric greenhouse gases. In turn, ocean biogeochemistry depends on numerous physical and biological processes that change over space and time. Accurately simulating these processes is fundamental for accurately simulating the ocean's role within the climate...

The vertical transport of surface water and carbon into ocean’s interior, known as subduction, is one of the main mechanisms through which the ocean influences Earth’s climate. New instrumental approaches have shown the occurrence of localized and intermittent subduction episodes associated with small-scale ocean circulation features. These studies...

The vertical transport of surface water and carbon into ocean's interior, known as subduction, is one of the main mechanisms through which the ocean influences Earth's climate. New instrumental approaches have shown the occurrence of localized and intermittent subduction episodes associated with small-scale ocean circulation features. These studies...

The Great Australian Bight (GAB), a coastal sea bordered by the Pacific, Southern and Indian Oceans, sustains one of the largest fisheries in Australia but the geographical origin of nutrients that maintain its productivity is not fully known. We use 12 years of modeled data from a coupled hydrodynamic and biogeochemical model and an Eulerian-Lagra...

The Southern Ocean has taken up more than 40% of the total anthropogenic carbon (Cant) stored in the oceans since the preindustrial era, mainly in subantarctic mode and intermediate waters (SAMW-AAIW). However, the physical mechanisms responsible for the transfer of Cant into the ocean interior remain poorly understood. Here, we use high resolution...

Atmospheric CO2 levels continue to rise, increasing the risk of severe impacts on the Earth system, and on the ecosystem services that it provides. Artificial Ocean Alkalization (AOA) is capable of reducing atmospheric CO2 concentrations, surface warming and addressing ocean acidification. Here we simulate global and regional responses to alkalinit...

The implications of a mesoscale eddy for relevant properties of the Southern Ocean carbon cycle is examined with in situ observations. We explored carbon properties inside a large (~190 km diameter) cyclonic eddy that detached from the Subantarctic Front (SAF) south of Tasmania in March 2016. Based on remote sensing, the eddy was present for ~2 mon...

Many baleen whales were commercially harvested during the 20th century almost to extinction. Reliable assessments of how this mass depletion impacted whale populations, and projections of their recovery, are crucial but there are uncertainties regarding the status of Southern Hemisphere whale populations. We developed a Southern Hemisphere spatial...

Over the last decade many climate models have evolved into Earth system models (ESMs), which are able to simulate both physical and biogeochemical processes through the inclusion of additional components such as the carbon cycle. The Australian Community Climate and Earth System Simulator (ACCESS) has been recently extended to include land and ocea...

Earth system models (ESMs) that incorporate carbon–climate feedbacks represent the present state of the art in climate modelling. Here, we describe the Australian Community Climate and Earth System Simulator (ACCESS)-ESM1, which comprises atmosphere (UM7.3), land (CABLE), ocean (MOM4p1), and sea-ice (CICE4.1) components with OASIS-MCT coupling, to...

Carbon-climate feedbacks have the potential to significantly impact the future climate by altering atmospheric CO2 concentrations (Zaehle et al., 2010). By modifying the future atmospheric CO2 concentrations, the carbon-climate feedbacks will also influence the future trajectory for ocean acidification. Here, we use the CO2 emissions scenarios from...

The Ocean Model Intercomparison Project (OMIP) focuses on the physics and biogeochemistry of the ocean component of Earth system models participating in the sixth phase of the Coupled Model Intercomparison Project (CMIP6). OMIP aims to provide standard protocols and diagnostics for ocean models, while offering a forum to promote their common assess...

Policy-and decision-makers require assessments of status and trends for marine species, habitats, and ecosystems to understand if human activities in the marine environment are sustainable, particularly in the face of global change. Central to many assessments are statistical and dynamical models of populations, communities, ecosystems, and their s...

Zooplankton are the intermediate trophic level between phytoplankton and fish, and are an important component of carbon and nutrient cycles, accounting for a large proportion of the energy transfer to pelagic fishes and the deep ocean. Given zooplankton's importance, models need to adequately represent zooplankton dynamics. A major obstacle, though...

The ocean's ability to store large quantities of carbon, combined with the millennial longevity over which this reservoir is overturned, has implicated the ocean as a key driver of glacial–interglacial climates. However, the combination of processes that cause an accumulation of carbon within the ocean during glacial periods is still under debate....

Skillful marine biogeochemical (BGC) models are required to understand a range of coastal and global phenomena such as changes in nitrogen and carbon cycles. The refinement of BGC models through the assimilation of variables calculated from observed in-water inherent optical properties (IOPs), such as phytoplankton absorption, is problematic. Empir...

Quantifying the surface to interior transport of Anthropogenic carbon (CA) is critical for projecting future carbon uptake and, for improved understanding of the role of the oceans in the global carbon cycle. Here we develop and apply a diagnostic tool that provides a volumetric streamfunction in (CA,σ0) coordinates to calculate the total diapycnal...

Mesoscale eddies in the south west Pacific region are prominent ocean features that represent distinctive environments for phytoplankton. Here we examine the seasonal plankton dynamics associated with averaged cyclonic and anticyclonic eddies (CE and ACE, respectively) off eastern Australia. We do this through building seasonal climatologies of mix...

This poster describes experiments using the CSIRO Mk3L climate system model that investigates the contribution of physical and biogeochemical changes that occurred in the glacial ocean to the net carbon storage of the ocean. We find that in order for the ocean to store a greater amount of carbon during glacial conditions, which explains the drawdow...

The Ocean Model Intercomparison Project (OMIP) focuses on the physics and biogeochemistry of the ocean component of Earth System Models participating in the sixth phase of the Coupled Model Intercomparison Project (CMIP6). OMIP aims to provide standard protocols and diagnostics for ocean models, while offering a forum to promote their common assess...

The ocean's ability to store large quantities of carbon, combined with the millennial longevity over which this reservoir is overturned, has implicated the ocean as a key driver of glacial-interglacial climates. However, the combination of processes that cause an accumulation of carbon within the ocean during glacial periods is still under debate....

Southern Ocean phytoplankton growth is limited by iron. Episodes of natural iron fertilisation are pivotal to triggering phytoplankton blooms in this region, the Kerguelen Plateau bloom being one prominent example. Numerous physical mechanisms that may supply iron to the euphotic zone in the Kerguelen Plateau region, and hence triggering a phytopla...

Climate influences marine ecosystems on a range of time scales, from weather-scale (days) through to climate-scale (hundreds of years). Understanding of interannual to decadal climate variability and impacts on marine industries has received less attention. Predictability up to 10 years ahead may come from large-scale climate modes in the ocean tha...

Dissolved Organic Carbon (DOC) is an important component in the global carbon cycle. It also plays an important role in influencing the coastal ocean biogeochemical (BGC) cycles and light environment. Studies focussing on DOC dynamics in coastal waters are data constrained due to the high costs associated with in situ water sampling campaigns. Sate...

Deliverables 2015-16: Trace gas measurements through Holocene to last glacial; Sensitivity of terrestrial carbon to climate (pre-industrial); Sensitivity of ocean carbon uptake to dust deposition; Carbon monoxide record for ACCESS chemistry (past century); Perfluorocarbons and halons over the past century.

Mesoscale eddies are ubiquitous features of ocean circulation that modulate the supply of nutrients to the upper sunlit ocean, influencing the rates of carbon fixation and export. The popular eddy-pumping paradigm implies that nutrient fluxes are enhanced in cyclonic eddies because of upwelling inside the eddy, leading to higher phytoplankton produ...

Over the last decade many climate models have evolved into earth system models (ESMs), which are able to simulate both physical and biogeochemical processes through the inclusion of additional components such as the carbon cycle. The Australian Community Climate and Earth System Simulator (ACCESS) has been recently extended to include land and ocea...

Skilful marine biogeochemical (BGC) models are required to understand a range of coastal and global phenomena such as changes in nitrogen and carbon cycles. The refinement of BGC models through the assimilation of variables calculated from observed in-water inherent optical properties (IOPs), such as phytoplankton absorption, is problematic. Empiri...

Ocean boundary currents, transporting water masses and marine biota along the coastlines, are important for regional climate and marine ecosystem functions. In this study, we review the dominant multi-decadal trends of ocean boundary currents around Australia. Using an eddy-resolving global ocean circulation model, this study has revealed that the...

Phytoplankton growth is the foundation for energy transfer into higher trophic levels, influences climate by the uptake of atmospheric CO2, and plays an important role in nutrient cycling. Here we use a novel lagrangian approach to characterize the nitrate supply to the Great Australian Bight, identify episodes of extreme phytoplankton blooms and a...

The Great Barrier Reef (GBR) is founded on reef-building corals. Corals build their exoskeletonwith aragonite, but ocean acidification is lowering the aragonite saturation state of seawater(Oa). The downscaling of ocean acidification projections from global to GBR scales requiresthe set of regional drivers controllingOato be resolved. Here we use a...

Supplementary Figures 1-8 and Supplementary Tables 1-2.

Eddy-resolving global ocean models are highly desired for spatially-improved climate studies, but this is challenging because they require careful configuration and substantial computational resources. Model drift, partially related to insufficient model spin-up, imperfect model physics or bias in surface forcing, can be problematic, leading to con...

Many coupled climate models suffer from large sea surface temperature (SST) biases in the tropical Pacific, and for this reason studies have used a combination of observed SSTs and model-generated SST warming patterns to obtain climate projections. However, the existence of biases in the present-day coupled model SSTs implies that SST future warmin...

Ocean acidification is a predictable consequence of rising atmospheric carbon dioxide (CO2), and is highly likely to impact the entire marine ecosystem-from plankton at the base of the food chain to fish at the top. Factors which are expected to be impacted include reproductive health, organism growth and species composition and distribution. Predi...

While the Northern Hemisphere sea-ice has uniformly declined over the past several decades, the observed sea-ice in the Southern Hemisphere has exhibited regions of increase and decrease. Here we use a comprehensive set of ocean-sea-ice simulations (1990-2007) to elucidate the drivers of the observed heterogeneous sea-ice trends. We show wind varia...

Earth System Models (ESMs) that incorporate carbon-climate feedbacks represent the present state of the art in climate modelling. Here, we describe the Australian Community Climate and Earth System Simulator (ACCESS)-ESM1 that combines existing ocean and land carbon models into the physical climate model to simulate exchanges of carbon between the...

Undoing the effects of continuing high carbon dioxide emissions on the oceans could take centuries, if it is possible at all.