Peat-based record from southern Patagonia shows centennial-scale variability since 4.2 ka

<p>Here we present a 4200-year-old high-resolution peat core reconstruction from southern Patagonia. Our detailed carbon isotope (δ13C) record and testate amoeba-inferred water table depth reconstruction point to a progressive wetting of the peatland surface from 4200 to 1500 cal. yr BP, followed by a dry event at 1200-800 cal. yr BP and drier conditions since then. Superimposed on this trend are centennial-scale dips in δ13C values and water table depths that we associate with warm/dry spells. We interpret these shifts, which are akin to positive phases of the Southern Annual Mode (SAM), as reflecting century-scale changes in the Southern Westerly Wind belt during the late Holocene. Other records from southern South America and Tasmania have revealed synchronous changes in local vegetation and fire activity, strengthening our hypothesis. We know that millennial-scale shifts in the Westerly winds influence ocean upwelling in the Southern Ocean, with effects on global atmospheric carbon dioxide (CO2) concentrations. Our study, along with a few others, may help elucidate whether centennial-scale SAM-like shifts could also modulate the global carbon cycle via CO2 degassing from the deep ocean. This is important because instrumental and reanalysis records indicate strengthening and poleward contraction indicate a positive phase of the SAM since the late twentieth century.</p>

Interannual Variability of Dinophysis acuminata and Protoceratium reticulatum in a Chilean Fjord: Insights from the Realized Niche Analysis

Here, we present the interannual distribution of Dinophysis acuminata and Protoceratium reticulatum over a 10-year period in the Reloncaví Fjord, a highly stratified fjord in southern Chile. A realized subniche approach based on the Within Outlying Mean Index (WitOMI) was used to decompose the species’ realized niche into realized subniches (found within subsets of environmental conditions). The interannual distribution of both D. acuminata and P. reticulatum summer blooms was strongly influenced by climatological regional events, i.e., El Niño Southern Oscillation (ENSO) and the Southern Annual Mode (SAM). The two species showed distinct niche preferences, with blooms of D. acuminata occurring under La Niña conditions (cold years) and low river streamflow whereas P. reticulatum blooms were observed in years of El Niño conditions and positive SAM phase. The biological constraint exerted on the species was further estimated based on the difference between the existing fundamental subniche and the realized subniche. The observed patterns suggested that D. acuminata was subject to strong biological constraint during the studied period, probably as a result of low cell densities of its putative prey (the mixotrophic ciliate Mesodinium cf. rubrum) usually observed in the studied area.

Annual climate summary Australia (2016): strong El Niño gives way to strong negative IOD.

Australian climate patterns and associated anomalies during 2016 are reviewed, with reference to relevant climate drivers for the Australian region. 2016 was the fourth-warmest year on record for Australia (annual anomaly of +0.87 °C), and the warmest year on record for the globe (the third year running that a new record has been set). Annual rainfall was above average for most of Australia, but below average for areas of the northern coasts between the Gascoyne in Western Australia and Townsville in Queensland, and pockets of coastal southeast Queensland and northeastern New South Wales.The very strong 2015–16 El Niño contributed to a very warm and dry first quarter. Autumn was the warmest on record nationally, with a significant nationwide heatwave occurring in late February to mid-March and bushfires at the start of the year in Victoria, Tasmania and Western Australia. In May the El Niño broke down and rainfall increased as a very strong negative Indian Ocean Dipole developed, lasting until November. While the central tropical Pacific approached La Niña thresholds during spring, a La Niña did not develop. The Southern Annual Mode commenced the year in a generally positive phase, was strongly positive in June and September, and was following by a strongly negative phase from late October until the end of the year.The period from May to September was record wet, relieving areas of drought in Queensland and southeastern Australia, but also causing flooding in multiple states. The last three months of the year saw a return to near-average rainfall and, while October and November were cooler than average for large areas, December was very warm for the eastern states.Ocean temperatures were also record warm for the Australian region during 2016, with an annual anomaly of +0.73 °C. Temperatures were particularly high during the first half of the year and resulted in widespread severe coral bleaching.

Tropospheric Rossby Wave Breaking and the SAM

An objective analysis of tropospheric anticyclonic- and cyclonic-breaking Rossby waves is performed for the Southern Hemisphere in austral summer (December–February) of 1979–2009. The climatology of both anticyclonic and cyclonic Rossby wave breaking (RWB) frequency is presented. The frequency of anticyclonic RWB is highest in an extended region of the Eastern Hemisphere on the anticyclonic side of the jet, while that of cyclonic RWB is highest on the cyclonic side of the jet. A composite analysis of anticyclonic and cyclonic RWB shows how they contribute to a positive and negative southern annual mode (SAM) index, respectively. The time series of austral summer anticyclonic RWB occurrence has a trend that closely matches the trend in the SAM index. Regions of RWB that are significantly correlated with the SAM index are objectively determined. Even though several such regions are identified, only two regions (anticyclonic and cyclonic) covering 17% of the area of the hemisphere are required in a linear regression model of the SAM index. The anticyclonic RWB region is zonally extended at 45°S and explains 78% of the variability of the summer-mean SAM index. The cyclonic region is located at high latitudes somewhat decoupled from the jet, in the longitudinal sector of the Indian Ocean. On synoptic time scales, transitions of the SAM index respond to RWB without time lag. ENSO cycles present an interesting zonal asymmetry to the distribution of Southern Hemispheric RWB in the central Pacific. Anticyclonic RWB is increased in the tropical/subtropical central Pacific during La Niña compared to El Niño. This increase is related to the strong local decrease in zonal wind. At the same time, anticyclonic RWB outside the central Pacific is increased in frequency poleward and decreased in frequency equatorward of 42°S, corresponding to a positive SAM index.