Table of Contents

• Coverage
• Dataset Description
  • Methods & Sampling
  • Data Processing Description
• Related Publications
• Parameters
• Instruments
• Project Information
• Funding

From 2014 to 2018, surface seawater samples from the Bermuda coral reef platform were collected every month at 0.5–1-m depth using a 5-L Niskin bottle. Samples were also collected along a transect between Bermuda and BATS in conjunction with BATS cruises. All parameters were collected following BATS methodology (Knap et al., 1996).

Samples for dissolved oxygen were collected in 140 ml Pyrex iodine flasks, stored in a dark location and the necks of the flasks were sealed with seawater. Samples were analyzed after 6-8 hours, based on the Strickland and Parsons (1968) modification of the Winkler (1888) method. Analysis was performed on an automated titration system using an UV light endpoint detection system as designed by the late Robert Williams of SIO. Prior to running the samples, a series of standards (6-8) and blanks (3-4) were run for determination of the thiosulphate normality value. Precision was typically <0.5 µmol kg-1.  

TA and DIC samples were collected according to standard protocols (Dickson et al., 2007) using 250-mL Kimax brand glass sample bottles. Samples were immediately poisoned with 100 μL saturated solution of HgCl2. DIC was analyzed coulometrically using a UIC CM5011 CO2 coulometer combined with a VINDTA3C (Marianda Inc) or SOMMA system, alternatively based on infrared absorption using an AIRICA (Marianda, Inc) and a Li-Cor 7000 as the detector. TA was analyzed based on potentiometric acid titrations (∼0.1 N HCl) using a VINDTA3S (Marianda Inc). Performance and precision of the instruments were regularly verified using certified reference material (CRM) prepared by A. Dickson at Scripps Institution of Oceanography (SIO). The accuracy and precision of replicate CRMs on any given day of analyses were typically in the range of ±2–4 μmol kg−1 for both TA and DIC.

Samples for nitrate+nitrite, nitrite, phosphate, silicic acid and ammonia were filtered through 0.8 µm Nuclepore filters then frozen (-20°C) in HDPE bottles until analysis. Samples were analyzed on a four channel SEAL AutoAnalyzer III using modified methods from Knap et al. (1996).   Analytical precision for triplicate nutrient measurements was approximately 0.03-0.05 µmoles kg-1. Certified standards from Ocean Scientific International were analyzed on a regular interval to maintain data quality.

Particulate Organic Carbon and Nitrogen (POC/PON) samples (2L) were filtered onto pre-combusted (450ºC, 5 hours) Whatman GF/F glass fiber filters (nominal pore size 0.7µm), and stored at -20°C.  Dried acidified samples were be combusted at 980 ºC on an Exeter Analytical Elemental Analyzer as described in Knap et al. (1996). Field blanks and acetanilide standards were run with each batch of samples. 

Phytoplankton pigment samples (4L) were filtered onto 25mm Whatman GF/F glass fiber filters, frozen in liquid nitrogen, and analyzed by both standard fluorometric and high performance liquid chromatography (HPLC) techniques. Samples were analyzed using the method of Bidigare et al. (2005) on an Agilent 1100 series HPLC. Samples were calculated based upon instrument response and retention times that were standardized annually with pigment standards obtained from Danish Hydraulic Institute.

Samples for bacterial abundance were collected in 50ml Falcon tubes then preserved with 0.2μm filtered formalin and stored at -80 °C. Direct counts of DAPI (4,6-Diaminino-2-phenylidole) stained cells were conducted using an epifluorscence microscope to determine abundance (Knap et al., 1996).

Salinity samples were collected in 250 ml borosilicate glass bottles (Ocean Scientific, UK) and analyzed using a Guildline Autosal 8400B. The salinometer were calibrated with standard seawater provided by Ocean Scientific, UK. Salinity was calculated based on the mean sample conductivity ratio from two separate measurements averaged over 5 seconds and computed according to the 1978 definition of Practical salinity (UNESCO, 1978). The precision of replicate samples was typically less than 0.001 psu.

Dissolved calcium samples were analyzed using a titration system developed by J. Ballard and Dr. T. Martz at SIO. Samples were collected in 100 ml plastic bottles. The dissolved calcium concentration was determined by EGTA titration with Zn-zincon as an indirect photometric indicator (Anfält and Granéli, 1976) using a custom photometric cell with a white LED, 620 nm filter, and photodiode. The voltage of the cell was monitored with Labview software and a 24-bit analog to digital converter (NI-9219). In the first step, 1 M borate buffer was added to 25 g of sample and diluted 10 fold. Zincon indicator (0.1%, 1ml) and equimolar Zn-EGTA (0.01 M, 2.5ml) were then added prior to an EGTA (0.02 M) gravimetric addition (~11 g) and software controlled volumetric additions (~0.1 ml).  Accuracy and precision of IAPSO standard seawater was in the range of 2-5 mol kg-1.

BCO-DMO Processing Notes:
- added conventional header with dataset name, PI name, version date
- modified parameter names to conform with BCO-DMO naming conventions
- prepended hhmm_in field with zeros when number of digits was less than 4.
- combined YYYYMMDD_in and hhmm_in fields to generate ISO_DateTime_UTC field.
- split Sample_id field to generate cruise_type, cruise_no, cast_no, and niskin_no fields.

NSF abstract:

Time-series observations from the Atlantic and Pacific Oceans have revealed indisputable evidence of long-term acidification of open-ocean surface seawater due to uptake of anthropogenic carbon dioxide from the atmosphere. Concurrent evidence of negative effects of acidification on the production and preservation of calcium carbonate have fueled concern about the potential consequences to coral reefs. Although long-term acidification in coral reef environments in general has not been observed, seawater acidification rates on the Bermuda coral reef platform between 2007-2012 have been found to be three times faster than the long-term (1983-2012) acidification rate observed at a nearby offshore open-ocean time-series station. The investigators on this project believe that they now understand how this happens and have designed a study to confirm or refute their ideas. Specifically they believe that the observed changes in 2007-2012 are attributable to a recent shift in reef metabolic processes associated with an increase in net reef calcification and heterotrophy. The evidence they have in-hand suggests that these changes have been fueled by an increase in food supply to the reef as a result of increased offshore primary production seemingly linked to the state of the North Atlantic Oscillation (NAO), a periodic back-and-forth shifting of atmospheric pressure differences between the subpolar and the subtropical North Atlantic. In this project, by collecting an extensive set of physical, chemical, and biological data extending from the reef platform at Bermuda to the offshore open-water time-series station, they will explore this idea.

The primary scientific and societal broader impacts of this project will be its relevance to advancing current understanding of the effects of ocean acidification on coral reefs. Robust prediction of future effects on this ecosystem requires knowledge of the main drivers of reef biogeochemical processes and of local seawater acidification. Secondly, the project will support the education and research activities of both graduate and undergraduate students working as members of the research team, and foster community educational outreach through the Ocean Discovery Institute in San Diego and the Ocean Academy in Bermuda to engage students from underrepresented minorities.

The central hypothesis of this research is that during years of negative winter NAO, intensified mixing and increased nutrient supply enhance offshore production leading to coral reef calcification and reef heterotrophy, thus intensifying the local seawater acidification on the reef. To address this hypothesis, the team will measure and characterize inshore seawater biogeochemical properties (temperature, salinity, dissolved inorganic carbon, total alkalinity, calcium, partial pressure of carbon dioxide, inorganic nutrients, particulate organic carbon and nitrogen, total organic carbon and nitrogen, phytoplankton pigments, and bacterial abundance) on a monthly interval across the Bermuda coral reef. These data will be evaluated in concert with data collected as part of the Bermuda-Atlantic Time-Series and Hydrostation S programs and along inshore-offshore transects. It is expected that this approach will further the understanding of how seawater biogeochemical properties, including seawater carbonate chemistry, vary over time and space on the Bermuda coral reef, and identify the main drivers of these variations. It will specifically address the coupling between offshore and inshore biogeochemical processes and how they are linked to larger-scale oceanographic and climatic forcings, such as the NAO. It also addresses how reef biogeochemical processes may alleviate or exacerbate ocean acidification, and whether these changes are important to reef metabolism in the context of other forcings such as light, nutrients, and food availability.

Based on the findings of the BEACON project, and especially the results published in Andersson et al. (Nature Climate Change, 4, 56-61, 2014) and Yeakel et al. (PNAS, 112, 14512-14517, 2015), BEACON II (https://www.bco-dmo.org/project/737955) aims to assess the links between offshore and reef biogeochemistry by continuing and expanding on the physical and chemical measurements on the Bermuda coral reef and in the surrounding Sargasso Sea.