Cenozoic Indo-Pacific warm pool controlled by both atmospheric CO2 and paleogeography.

The Indo-Pacific warm pool (IPWP) is crucial for regional and global climates. However, the development of the IPWP and its effect on the regional climate during the Cenozoic remain unclear. Here, using a compilation of sea surface temperature (SST) records (mainly since the middle Miocene) and multimodel paleoclimate simulations, our results indicated that the extent, intensity and warmest temperature position of the IPWP changed markedly during the Cenozoic. Specifically, its extent decreased, its intensity weakened, and its warmest temperature position shifted from the Indian to western Pacific Ocean over time. The atmospheric CO2 dominated its extent and intensity, while paleogeography, by restricting the distribution of the Indian Ocean and the width of the tropical seaways, controlled the shift in its warmest temperature position. In particular, the eastward shift to the western Pacific Ocean from the middle to late Miocene inferred from compiled SST records likely resulted from the constriction of tropical seaways. Furthermore, by changing the atmospheric thermal structure and atmospheric circulation, the reduced extent and intensity of the IPWP decreased the annual precipitation in the western Indian Ocean, eastern Asia and Australia, while the shift in the warmest temperature position from the Indian to western Pacific Ocean promoted aridification in Australia. Qualitative model-data agreements are obtained for both the IPWP SST and regional climate. From the perspective of past warm climates with high concentrations of atmospheric CO2, the expansion and strengthening of the IPWP will occur in a warmer future and favor excessive precipitation in eastern Asia and Australia.

Effects of meteo-oceanographic conditions on the weathering processes of oil spills in northeastern Brazil.

This paper presents the graphical results of the Lagrangian-model and the weathering processes associated with oil spills in the tropical South Atlantic, taking into account the meteorological and oceanographic conditions of the study region. The scenarios were created in the Brazilian-NE waters adjacent, with simulation times of 670 h, and densities of 35, 25, and 15API with volume of 1590 m3 were considered. The main results showed that the meteo-oceanographic characteristics of the study region influence the trajectories and weathering processes in the oil spill. The trajectories varied for each launch point and reached the continent severely in January and October. The associated weathering processes showed higher rates in September and lower rates in April, indicative of the influence of phenomena such as Intertropical Tropical Convergence Zone and warm pool in the South Atlantic region. Sea surface temperature and wind speed are key factors that correlate positively with these months.

Latitudinal and meridional patterns of picophytoplankton variability are contrastingly associated with Ekman pumping and the warm pool in the tropical western Pacific.

Marine picophytoplankton plays a major role in marine cycling and energy conversion, and its effects on the carbon cycle and global climate change have been well documented. In this study, we investigated the response of picophytoplankton across a broad range of physicochemical conditions in two distinct regions of the tropical western Pacific. Our analysis considered the abundance, carbon biomass, size fraction, distribution, and regulatory factors of the picophytoplankton community, which included the cyanobacteria Prochlorococcus and Synechococcus, and small eukaryotic phytoplankton (picoeukaryotes). The first region was a latitudinal transect along the equator (142-163° E, 0° N), characterized by stratified oligotrophic conditions. The second region was a meridional transect (143° E, 0-22° N) known for its high-nutrient and low-chlorophyll (HNLC) conditions. Results showed that picophytoplankton contributed >80% of the chlorophyll a (Chl a), and was mainly distributed above 100 m. Prochlorococcus was the dominant organism in terms of cell abundance and estimated carbon biomass in both latitudinal and meridional transects, followed by Synechococcus and picoeukaryotes. In the warm pool, Prochlorococcus was primarily distributed below the isothermal layer, with the maximum subsurface abundance forming below it. The maximum Synechococcus abundance was restricted to the west-warm pool, due to the high temperature, and the second-highest Synechococcus abundance was associated with frontal interaction between the east-warm pool and the westward advance of Middle East Pacific water. In contrast, picoeukaryotes formed a maximum subsurface abundance corresponding to the subsurface Chl a maximum. In the mixed HNLC waters, the cell abundance and biomass of the three picophytoplankton groups were slightly lower than those in the warm pool. Due to a cyclonic eddy, the contours of the maximum subsurface Prochlorococcus abundance were uplifted, evidently with a lower value than the surrounding water. Synechococcus abundance varied greatly in patches, forming a weakly high subsurface peak when the isothermal layer rose to the near-surface (<50 m). The subsurface maximum picoeukaryote abundance was also highly consistent with that of the subsurface Chl a maximum. Correlation analysis and generalized additive models of environmental factors showed that nutrient availability had a two-faceted role in regulating the spatial patterns of picophytoplankton in diverse latitudinal and meridional environments. We concluded through regression that temperature and light irradiance were the key determinants of picophytoplankton variability in the tropical western Pacific. This study provides insights into the changing picophytoplankton community structure with potential future changing hydroclimatic force.

Oceanic and atmospheric anomalies associated with extreme precipitation events in China 1983-2020.

Observed synoptic anomalies in connection with China's extreme precipitation events/floods in the summers of 1982/83, 1997/98, 2010, 2014, 2015/16, and 2020 are studied. These events mainly occur within the middle and lower Yangtze basins. The dominant moisture source is the Northern Indian Ocean and the Southwestern Pacific Ocean of the Indo-Pacific warm pool (IPWP). Both of these bodies of water have warmed since 1979. In East Asia, the strong land-sea thermal contrast driven by global warming drives the increased East Asian summer monsoon (EASM) circulation, which develops deep convective precipitation. The total precipitable water in the Indo-Pacific region has also been increasing since 1979. The intense southwest Indian monsoon transports moist air to the Yangtze basin in mid-June and forms the Meiyu (plum rain) front. Strengthened Okhotsk/Ural blocking highs in East and West Asia, as well as the Western Pacific subtropical high (WPSH) and the South Asian high (SAH) over south Eurasia, remain stationary for long periods and interact to exacerbate the precipitation. The western edge of the WPSH expands westward towards East Asia to transport moisture. To the north, the WPSH combines with the two blocking highs to trigger more rain. The intensified SAH expands eastward and merges with the extended WPSH to add rain. On the other hand, rainfall is modulated by the El Niño-Southern Oscillation (ENSO), notably in relation to the super El Niño events in 1982-1983, 1997-1998, 2015-2016, and 2020. The research described in this paper highlights changes in the weather systems with warming and, in particular, the enormous and dominating impact of the warming and expanding IPWP on rainfall extremes. Improved seasonal forecasts and planning ahead will protect lives and livelihoods.

Atmospheric concentrations and sources of black carbon over tropical Australian waters.

Black carbon (BC) aerosols significantly contribute to radiative budgets globally, however their actual contributions remain poorly constrained in many under-sampled ocean regions. The tropical waters north of Australia are a part of the Indo-Pacific warm pool, regarded as a heat engine of global climate, and are in proximity to large terrestrial sources of BC aerosols such as fossil fuel emissions, and biomass burning emissions from northern Australia. Despite this, measurements of marine aerosols, especially BC remain elusive, leading to large uncertainties and discrepancies in current chemistry-climate models for this region. Here, we report the first comprehensive measurements of aerosol properties collected over the tropical warm pool in Australian waters during a voyage in late 2019. The non-marine related aerosol emissions observed in the Arafura Sea region were more intense than in the Timor Sea marine region, as the Arafura Sea was subject to greater continental outflows. The median equivalent BC (eBC) concentration in the Arafura Sea (0.66 µg m-3) was slightly higher than that in the Timor Sea (0.49 µg m-3). Source apportionment modelling and back trajectory analysis and tracer studies consistently suggest fossil fuel combustion eBC (eBCff) was the dominant contributor to eBC across the entire voyage region, with biomass burning eBC (eBCbb) making significant additional contributions to eBC in the Arafura Sea. eBCff (possibly from ship emissions or oil and gas rigs and their associated activities) and cloud condensation nuclei (CCN) were robustly correlated in the Timor Sea data, whereas eBCbb positively correlated to CCN in the Arafura Sea, suggesting different sources and atmospheric processing pathways occurred in these two regions. This work demonstrates the substantial impact that fossil fuel and biomass burning emissions can have on the composition of aerosols and cloud processes in the remote tropical marine atmosphere, and their potentially significant contribution to the radiative balance of the rapidly warming Indo-Pacific warm pool.

Global vegetation productivity responses to the West Pacific Warm Pool.

Sea surface temperatures (SSTs) strongly influence atmospheric circulation and the Earth's climate, which in turn significantly affects vegetation productivity. Most of the previous studies on the subject have focused on links between the El Niño-Southern Oscillation (ENSO) and vegetation productivity, but few studies have addressed the effects of West Pacific Warm Pool (WPWP) on that although the early stages of the ENSO phenomenon may first develop there. In this paper, we use the mean SST values in the WPWP to construct a climate index, known as the WPWP index (WPI), and study the impacts of the WPWP on global vegetation productivity. We provide evidence for a robust link among the alternating warm and cool WPI pattern, terrestrial vegetation productivity and carbon balance. The analysis is based on both satellite observations and model simulations. The results of this study show that the warm and cool WPWP phases have inverse effects on land surface temperature and precipitation. A warm (cool) WPWP is associated with a warmer (cooler) climate on global land surfaces as well as a drier (wetter) climate in southern hemisphere, and hence enhances (suppresses) vegetation productivity in the latitudes of approximately 10-70°N and suppresses (enhances) vegetation growth in the latitudes of approximately 10-30°S. The underlying mechanism is also discussed. The WPI serves as a meaningful climate index for studying the ocean-vegetation teleconnections.

Forcing Single-Column Models Using High-Resolution Model Simulations.

To use single-column models (SCMs) as a research tool for parameterization development and process studies, the SCM must be supplied with realistic initial profiles, forcing fields, and boundary conditions. We propose a new technique for deriving these required profiles, motivated by the increase in number and scale of high-resolution convection-permitting simulations. We suggest that these high-resolution simulations be coarse grained to the required resolution of an SCM, and thereby be used as a proxy for the true atmosphere. This paper describes the implementation of such a technique. We test the proposed methodology using high-resolution data from the UK Met Office's Unified Model, with a resolution of 4 km, covering a large tropical domain. These data are coarse grained and used to drive the European Centre for Medium-Range Weather Forecast's Integrated Forecasting System (IFS) SCM. The proposed method is evaluated by deriving IFS SCM forcing profiles from a consistent T639 IFS simulation. The SCM simulations track the global model, indicating a consistency between the estimated forcing fields and the true dynamical forcing in the global model. We demonstrate the benefits of selecting SCM forcing profiles from across a large domain, namely, robust statistics, and the ability to test the SCM over a range of boundary conditions. We also compare driving the SCM with the coarse-grained data set to driving it using the European Centre for Medium-Range Weather Forecast operational analysis. We conclude by highlighting the importance of understanding biases in the high-resolution data set and suggest that our approach be used in combination with observationally derived forcing data sets.

Human-caused Indo-Pacific warm pool expansion.

The Indo-Pacific warm pool (IPWP) has warmed and grown substantially during the past century. The IPWP is Earth's largest region of warm sea surface temperatures (SSTs), has the highest rainfall, and is fundamental to global atmospheric circulation and hydrological cycle. The region has also experienced the world's highest rates of sea-level rise in recent decades, indicating large increases in ocean heat content and leading to substantial impacts on small island states in the region. Previous studies have considered mechanisms for the basin-scale ocean warming, but not the causes of the observed IPWP expansion, where expansion in the Indian Ocean has far exceeded that in the Pacific Ocean. We identify human and natural contributions to the observed IPWP changes since the 1950s by comparing observations with climate model simulations using an optimal fingerprinting technique. Greenhouse gas forcing is found to be the dominant cause of the observed increases in IPWP intensity and size, whereas natural fluctuations associated with the Pacific Decadal Oscillation have played a smaller yet significant role. Further, we show that the shape and impact of human-induced IPWP growth could be asymmetric between the Indian and Pacific basins, the causes of which remain uncertain. Human-induced changes in the IPWP have important implications for understanding and projecting related changes in monsoonal rainfall, and frequency or intensity of tropical storms, which have profound socioeconomic consequences.

Flyingfish feeding ecology in the eastern Pacific: prey partitioning within a speciose epipelagic community.

To test the hypothesis that prey partitioning contributes to community stability in flyingfish, the gut contents of 359 flyingfish specimens (representing five genera and eight species within Exocoetidae and Hemiramphidae) were collected at 50 dip-net stations during hour-long night-time fishing in oceanic waters of the eastern tropical Pacific Ocean between August and November 2007. Analyses using multidimensional scaling, and analysis of similarity revealed significant dietary differences among species, and similarity percentages tests helped identify the specific prey taxa responsible for these differences. Six species specialized on copepods (58·3-96·9% by number), but targeted different families. Specifically, the barbel flyingfish Exocoetus monocirrhus (n = 205) focused on euchaetids (51·6%), the banded flyingfish Hirundichthys marginatus (n = 24) fed on pontellids (21·8%), while the tropical two-wing flyingfish Exocoetus volitans (n = 11) and the bigwing halfbeak Oxyporhamphus micropterus (n = 34) ingested calanoids (54·6 and 17·0%). In contrast, the whitetip flyingfish Cheilopogon xenopterus (n = 73) and the mirrorwing flyingfish Hirundichthys speculiger (n = 4) had generalized diets comprising similar proportions of amphipod, copepod, mollusc and larval fish prey. Distinct differences in mean fullness, highly digested material, per cent empty guts and mean numbers of prey per gut were also synthesized, and uncovered a pattern of asynchronous feeding. Altogether, these findings provide valuable descriptive data on the diets of an understudied group of epipelagic teleosts, and, by extension, suggest that prey partitioning (taxa and feeding times) may influence flyingfish feeding ecology by reducing interspecific competition.