Coral-based climate records from tropical South Atlantic: 2009/2010 ENSO event in C and O isotopes from Porites corals (Rocas Atoll, Brazil)

Abstract

Coral skeletons contain records of past environmental conditions due to their long life span and well calibrated geochemical signatures. C and O isotope records of corals are especially interesting, because they can highlight multidecadal variability of local climate conditions beyond the instrumental record, with high fidelity and sub-annual resolution. Although, in order to get an optimal geochemical signal in coral skeleton, sampling strategies must be followed. Here we report one of the first coral-based isotopic record from the Equatorial South Atlantic from two colonies of Porites astreoides from the Rocas Atoll (offshore Brazil), a new location for climate reconstruction. We present time series of isotopic variation from profiles along the corallite valley of one colony and the apex of the corallite fan of the other colony. Significant differences in the isotopic values between the two colonies are observed, yet both record the 2009/2010 El Niño event -a period of widespread coral bleaching -as anomalously negative δ18 O values (up to −1 permil). δ 13 C is found to be measurably affected by the El Niño event in one colony, by more positive values (+0.39 ‰), and together with a bloom of endolithic algae, may indicate physiological alteration of this colony. Our findings indicate that corals from the Rocas Atoll can be used for monitoring climate oscillations in the tropical South Atlantic Ocean.

Endolithic Algae Affect Modern Coral Carbonate Morphology and Chemistry

“…The study of Hartmann et al (2010) interpreted the formation of green bands as endolithic algal blooms during episodes of environmental heat stress inducing coral bleaching. An increased endolithic algae activity could lead to more pronounced metabolic fractionation of CO 2 manifesting as a locally more positive δ 13 C value of the coral carbonate (Pereira et al, 2015), thus recording environmental stress events. The intracrystalline organic matter of endolithic algae as total hydrolyzable amino acid (THAA) carbon (Gupta et al, 2007) is preserved over centuries in coral skeletons (Ingalls et al, 2003), adding to the established approaches used in paleoceanograpic research.…”

Scientific diving in Brazil: history, present and perspectives

“…First used in 2003 (Santedicola, 2008), underwater coring of corals and reefs has been conduct to obtain samples to understand the mechanism of coral calcification (Oliveira et al, 2008;Kikuchi et al, 2013), paleoceanographic studies (Santedicola, 2008;Kikuchi et al, 2013;Pereira et al, 2015Pereira et al, , 2018, sea level reconstruction, and reef evolution (Bastos et al, 2018). The techniques used in these studies are underwater navigation, operating percussion, and pneumatic (Santedicola, 2008;Kikuchi et al, 2013;Pereira et al, 2015Pereira et al, , 2018 or hydraulic drilling accessories and equipment.…”

“…First used in 2003 (Santedicola, 2008), underwater coring of corals and reefs has been conduct to obtain samples to understand the mechanism of coral calcification (Oliveira et al, 2008;Kikuchi et al, 2013), paleoceanographic studies (Santedicola, 2008;Kikuchi et al, 2013;Pereira et al, 2015Pereira et al, , 2018, sea level reconstruction, and reef evolution (Bastos et al, 2018). The techniques used in these studies are underwater navigation, operating percussion, and pneumatic (Santedicola, 2008;Kikuchi et al, 2013;Pereira et al, 2015Pereira et al, , 2018 or hydraulic drilling accessories and equipment. In situ studies on coral calcification were conducted by coral skeleton staining (Kikuchi et al, 2013), while studies on reef sedimentation rates (Dutra et al, 2006;Segal and Castro, 2011) required choosing suitable sites to install sediment traps and returning periodically to replace the devices.…”

“…Obtaining longer core samples, at depths down to 1 m, requires pneumatic or hydraulic equipment (Figure 7B). This involves adapting power drills to cylinders attached to tanks that are taken to the bottom to be operated (Pereira et al, 2015(Pereira et al, , 2018. Another alternative to pneumatic (Santedicola, Scientific diving in Brazil Ocean and Coastal Research 2023, v71:e23045 13 or hydraulic equipment are compressors or pumps installed on vessels.…”