Implications of salinity normalization of seawater total alkalinity in coral reef metabolism studies

Salinity normalization of total alkalinity (TA) and dissolved inorganic carbon (DIC) data is commonly used to account for conservative mixing processes when inferring net metabolic modification of seawater by coral reefs. Salinity (S), TA, and DIC can be accurately and precisely measured, but salinity normalization of TA (nTA) and DIC (nDIC) can generate considerable and unrecognized uncertainties in coral reef metabolic rate estimates. While salinity normalization errors apply to nTA, nDIC, and other ions of interest in coral reefs, here, we focus on nTA due to its application as a proxy for net coral reef calcification and the importance for reefs to maintain calcium carbonate production under environmental change. We used global datasets of coral reef TA, S, and modeled groundwater discharge to assess the effect of different volumetric ratios of multiple freshwater TA inputs (i.e., groundwater, river, surface runoff, and precipitation) on nTA. Coral reef freshwater endmember TA ranged from -2 up to 3032 μmol/kg in hypothetical reef locations with freshwater inputs dominated by riverine, surface runoff, or precipitation mixing with groundwater. The upper bound of freshwater TA in these scenarios can result in an uncertainty in reef TA of up to 90 μmol/kg per unit S normalization if the freshwater endmember is erroneously assumed to have 0 μmol/kg alkalinity. The uncertainty associated with S normalization can, under some circumstances, even shift the interpretation of whether reefs are net calcifying to net dissolving, or vice versa. Moreover, the choice of reference salinity for normalization implicitly makes assumptions about whether biogeochemical processes occur before or after mixing between different water masses, which can add uncertainties of ±1.4% nTA per unit S normalization. Additional considerations in identifying potential freshwater sources of TA and their relative volumetric impact on seawater are required to reduce uncertainties associated with S normalization of coral reef carbonate chemistry data in some environments. However, at a minimum, researchers should minimize the range of salinities over which the normalization is applied, precisely measure salinity, and normalize TA values to a carefully selected reference salinity that takes local factors into account.

Method for Forecasting the Efficiency of Matrix Acid Treatment of Carbonate

In the international practice of developing hydrocarbon fields, one of the most common methods of influencing the bottomhole formation zone to stimulate the inflow is acid treatment. Despite the significant accumulated experience, subsoil users increasingly face with a decrease in planned and actual increases in production rates after this type of measures, which is due to both the deterioration of the resource base and the adoption of erroneous decisions during their design. It is necessary to scientifically substantiate the design of acid treatments, taking into account individual well conditions and a preliminary assessment of their effectiveness to reduce technological and economic risks. This study presents a method for predicting the result of acid stimulation on the formation based on multivariate regression analysis and laboratory studies on rock samples. Its approbation was carried out on the example of a carbonate production facility of an oil field in the Perm Krai. The obtained statistical dependencies made it possible to determine with high accuracy the potential success of the planned geological and technical measures, to give recommendations on their adjustment to achieve the target indicators. In the course of laboratory experiments, the optimal technological parameters of the impact were identified: the prospects of multi-volume acid treatments were established with the exclusion of the stage of acid aging for the reaction. The integration of the results of mathematical and physical modeling made it possible to select the required design of acid treatments in relation to the considered geological and physical conditions and assess their expected technological efficiency. The developed technique can be used to rank candidate wells, form and adjust targeted programs for geological and technical measures for short and long term periods, and determine the stimulation technology. The described algorithm can be successfully replicated to other fields.

Paleo-oceanographic and -climatic reconstruction in the Southwest Pacific [ODP Site 1123] during MIS 11

<p>Marine Isotope Stage 11 [424 to 374 ka] is unique compared to most other recent Quaternary interglacial periods due to its duration and orbital geometry, both of which have previously been cited as evidence that MIS 11 may be a suitable analogue to project future climate. This study aims to evaluate this prolonged warm period at a key site in the sparsely studied Southwest Pacific Ocean at Ocean Drilling Program [ODP] 1123. This cored site, situated at 3290 m water depth on the northern flank of the Chatham Rise, straddles the northern limit of the modern Subtropical Front, 1100 km east of New Zealand, where sediments record strong subtropical and subpolar signals over interglacial to glacial cycles. Two species of planktonic foraminifera were analysed, Globigerinoides ruber and Globigerina bulloides [Gs. ruber and Gg. bulloides], for trace elements and size-normalised test weights [SNW; Gg. bulloides only] in order to reconstruct ocean temperature, chemistry, structure and circulation during MIS 11. Gg. bulloides was found to have anomalously low SNW [~50% compared to modern specimens] implying either [i] poor calcification environment due to low CO₃⁻² concentrations, or [ii] post-mortem alteration either in the deep water column or ocean floor environment. Traditional dissolution proxies for ODP 1123 do not indicate significant dissolution during MIS 11. Nevertheless, the inception of modern carbonate platforms and reefs at this time leads to the hypothesis that CO₃⁻² concentrations in the surface ocean were low due to a shifting in the locus of carbonate production, and this is a potential cause, amongst other possibilities, of the low SNW in Gg. bulloides. However, calcification in a low CO₃⁻² concentration ocean does not appear to have significantly affected the geochemical proxies utilised in this study [Mg/Ca-derived paleo-ocean temperatures, δ¹⁸O and micro-nutrients Mn/Ca and Zn/Ca ratios as water-mass tracers] based on comparison with a similar study on younger sediments in the same core. The temperature difference between Gs. ruber and Gg. bulloides is the same as the modern temperature difference at ODP 1123, implying that Gs.ruber was also not markedly affected by either low CO₃⁻² concentrations during calcification or post-mortem dissolution. Laser ablation inductively coupled plasma mass spectrometry is utalised to measure in situ trace element ratios [Mg, Al, Ca, Mn, Zn and Sr/Ca], and reconstruct the thermal structure of the ocean’s upper 200 m. The main findings are [i] a well stratified upper ocean in warm periods punctuated by well mixed waters in cooler and presumably windier conditions; [ii] an invigorated South Pacific Gyre during the prolonged MIS 11 interglacial, resulting in a greater inflow of subtropical water to ODP 1123 as evinced by Mn/Ca and Zn/Ca ratios and supported by elevated subtropical foramiferal assemblages; [iii] paleo-ocean temperatures that indicate the mean MIS 11 sea surface temperature optimum was ca. 2°C warmer than present; and [iv] a spike in productivity is identified by elevated Mn/Ca and Zn/Ca ratios at ca. 400 ka, coinciding with a spike in eutrophic species abundance, indicating a period of significantly enhanced subtropical water influence. Records from other New Zealand sites reveal MIS 11 as a prolonged [up to 40 kyr] interglacial period, following a rapid and pronounced 10°C warming from the MIS 12 glacial. Deglaciation occurred 13 kyr earlier than the global benthic record. This rise was punctuated by an Antarctic Cold Reversal-like cooling confirming episodic sub-polar influences at the site. Some differences between the orbital configurations of MIS 1 and 11, particularly at the precessional scale, coupled with apparently unusual ocean chemistry [e.g., low CO₃⁻²] during MIS 11, suggest that MIS 11 may not be an ideal analogue for the Holocene.</p>

Paleo-oceanographic and -climatic reconstruction in the Southwest Pacific [ODP Site 1123] during MIS 11

<p>Marine Isotope Stage 11 [424 to 374 ka] is unique compared to most other recent Quaternary interglacial periods due to its duration and orbital geometry, both of which have previously been cited as evidence that MIS 11 may be a suitable analogue to project future climate. This study aims to evaluate this prolonged warm period at a key site in the sparsely studied Southwest Pacific Ocean at Ocean Drilling Program [ODP] 1123. This cored site, situated at 3290 m water depth on the northern flank of the Chatham Rise, straddles the northern limit of the modern Subtropical Front, 1100 km east of New Zealand, where sediments record strong subtropical and subpolar signals over interglacial to glacial cycles. Two species of planktonic foraminifera were analysed, Globigerinoides ruber and Globigerina bulloides [Gs. ruber and Gg. bulloides], for trace elements and size-normalised test weights [SNW; Gg. bulloides only] in order to reconstruct ocean temperature, chemistry, structure and circulation during MIS 11. Gg. bulloides was found to have anomalously low SNW [~50% compared to modern specimens] implying either [i] poor calcification environment due to low CO₃⁻² concentrations, or [ii] post-mortem alteration either in the deep water column or ocean floor environment. Traditional dissolution proxies for ODP 1123 do not indicate significant dissolution during MIS 11. Nevertheless, the inception of modern carbonate platforms and reefs at this time leads to the hypothesis that CO₃⁻² concentrations in the surface ocean were low due to a shifting in the locus of carbonate production, and this is a potential cause, amongst other possibilities, of the low SNW in Gg. bulloides. However, calcification in a low CO₃⁻² concentration ocean does not appear to have significantly affected the geochemical proxies utilised in this study [Mg/Ca-derived paleo-ocean temperatures, δ¹⁸O and micro-nutrients Mn/Ca and Zn/Ca ratios as water-mass tracers] based on comparison with a similar study on younger sediments in the same core. The temperature difference between Gs. ruber and Gg. bulloides is the same as the modern temperature difference at ODP 1123, implying that Gs.ruber was also not markedly affected by either low CO₃⁻² concentrations during calcification or post-mortem dissolution. Laser ablation inductively coupled plasma mass spectrometry is utalised to measure in situ trace element ratios [Mg, Al, Ca, Mn, Zn and Sr/Ca], and reconstruct the thermal structure of the ocean’s upper 200 m. The main findings are [i] a well stratified upper ocean in warm periods punctuated by well mixed waters in cooler and presumably windier conditions; [ii] an invigorated South Pacific Gyre during the prolonged MIS 11 interglacial, resulting in a greater inflow of subtropical water to ODP 1123 as evinced by Mn/Ca and Zn/Ca ratios and supported by elevated subtropical foramiferal assemblages; [iii] paleo-ocean temperatures that indicate the mean MIS 11 sea surface temperature optimum was ca. 2°C warmer than present; and [iv] a spike in productivity is identified by elevated Mn/Ca and Zn/Ca ratios at ca. 400 ka, coinciding with a spike in eutrophic species abundance, indicating a period of significantly enhanced subtropical water influence. Records from other New Zealand sites reveal MIS 11 as a prolonged [up to 40 kyr] interglacial period, following a rapid and pronounced 10°C warming from the MIS 12 glacial. Deglaciation occurred 13 kyr earlier than the global benthic record. This rise was punctuated by an Antarctic Cold Reversal-like cooling confirming episodic sub-polar influences at the site. Some differences between the orbital configurations of MIS 1 and 11, particularly at the precessional scale, coupled with apparently unusual ocean chemistry [e.g., low CO₃⁻²] during MIS 11, suggest that MIS 11 may not be an ideal analogue for the Holocene.</p>

An emerging coral disease outbreak decimated Caribbean coral populations and reshaped reef functionality

Diseases are major drivers of the deterioration of coral reefs, linked to major declines in coral abundance, reef functionality, and reef-related ecosystems services1-3. An outbreak of a new disease is currently rampaging through the populations of the remaining reef-building corals across the Caribbean region. The outbreak was first reported in Florida in 2014 and reached the northern Mesoamerican reef by summer 2018, where it spread across the ~ 450-km reef system only in a few months4. Rapid infection was generalized across all sites and mortality rates ranged from 94% to < 10% among the 21 afflicted coral species. This single event further modified the coral communities across the region by increasing the relative dominance of weedy corals and reducing reef functionality, both in terms of functional diversity and calcium carbonate production. This emergent disease is likely to become the most lethal disturbance ever recorded in the Caribbean, and it will likely result in the onset of a new functional regime where key reef-building and complex branching acroporids (a genus apparently unaffected) will once again become conspicuous structural features in reef systems with yet even lower levels of physical functionality.

The Permian–Triassic boundary section at Baghuk Mountain, Central Iran: carbonate microfacies and depositional environment

Sections at Baghuk Mountain, 45 km NNW of Abadeh (Central Iran), have excellent exposures of fossiliferous marine Late Permian to Early Triassic sedimentary successions. Detailed bed-by-bed sampling enables the analysis of microfacies changes of three successive rock units across the Permian–Triassic boundary. The Late Permian Hambast Formation is mainly the result of biogenic carbonate production. Its carbonate microfacies is dominated by biogen-rich and bioturbated nodular limestones, indicating a well-oxygenated aphotic to dysphotic environment. The biogen-dominated carbonate factory in the Permian ceased simultaneously with the main mass extinction pulse, which is marked by a sharp contact between the Hambast-Formation and the overlaying Baghuk Member (= ‘Boundary Clay’). The clay and silt deposits of the Baghuk Member with some carbonate beds show only a few signs of bioturbation or relics of benthic communities. The Early Triassic Claraia Beds are characterised by a partly microbially induced carbonate production, which is indicated by frequent microbialite structures. The depositional environment does not provide evidence of large amplitude changes of sea level or subaerial exposure during the Permian–Triassic boundary interval. The deposition of the Baghuk Mountain sediments took place in a deep shelf environment, most of the time below the storm wave base.