A 3-year time series of volatile organic iodocarbons in Bedford Basin, Nova Scotia: a northwestern Atlantic fjord

Abstract

Abstract. We report weekly observations of volatile organic iodocarbons (CH3I, CH2ClI and CH2I2) over the time period May 2015 to December 2017 from four depths in Bedford Basin, a coastal fjord (70 m deep) on the Atlantic coast of Canada. The fjord is subject to wintertime mixing, seasonal stratification and bloom dynamics, subsurface oxygen depletion, local input of freshwater, and occasional intrusions of higher-density water from the adjacent continental shelf. Near-surface concentrations showed strong seasonal and sub-seasonal variability, which is compared with other coastal time series. The vertical variation of CH2I2 and CH2ClI within the upper 10 m is consistent with rapid photolysis of CH2I2. Average annual sea-to-air fluxes (46.7 nmol m−2 day−1) of total volatile organic iodine were similar to those observed in other coastal and shelf time series, and polyiodinated compounds contributed 80 % of the total flux. Fluxes were subject to strong interannual variability (a factor of 2) mainly due to wind speed variability. Near-surface net production of CH3I averaged 1 pmol L−1 day−1 and was similar to rates in the English Channel but an order of magnitude higher than in shallow waters of the Kiel Fjord, Germany, possibly due to higher microbial degradation in the latter. The near-bottom (60 m) time series showed evidence of CH3I production associated with organic matter degradation and a possible “switch” from the production of CH3I via an alkylation pathway to the production of CH2I2 by a haloform-type reaction. Near-bottom CH3I production varied strongly between years but was generally ca. 20 times lower than near-surface production.

Physical mixing in coastal waters controls and decouples nitrification via biomass dilution

“…1 and 2 A ). In July 2017, there was an intrusion of shelf water to mid-depth layers (∼30 m) of BB ( 44 ). Some of this intruding water was entrained into the bottom layers during the subsequent weeks, as indicated by nitrate decrease and a transient delay in oxygen decrease at 60 m (Event MDI17, Fig.…”

Two chemistries on a single lab-on-chip: Nitrate and orthophosphate sensing underwater with inlaid microfluidics

“…Figure 1B shows a photograph of the sensor package during the deployment, resting on the bottom of the river. Fish Hatchery Park is located at the northern inlet of the Bedford Basin (Figure 1C) and connects the basin to the Sackville River, which acts as the primary freshwater source to the basin (Kepkay et al, 1993;Shi and Wallace, 2018). To permit maximum sampling frequency, expanded fluid reservoirs were tied to the sensor without use of a reagent canister.…”

Characterization of nitrogen isotope fractionation during nitrification based on a coastal time series

“…In addition, in mid‐July 2017, an intrusion to the mid‐depths of the basin brought more saline water (Fig. 3d; see also Shi and Wallace 2018). This coincided with a slower oxygen decrease at 60 m (Fig.…”

“…3a–f). Occasional shelf water intrusion events occur in many years, interrupting the isolation of the bottom water during the stratified period by introducing relatively warm, saline, nutrient‐poor and oxygen‐rich water from the Scotian Shelf into the bottom or mid‐depths of the basin (Platt et al 1972; Burt et al 2013; Shi and Wallace 2018).…”

“…The shelf‐water intrusion events of July 2014 and July 2017 (intrusion to mid‐depth; Shi and Wallace 2018) were modeled in the same way as winter mixing (Haas et al 2021), but the concentrations and δ 15 N values of the DIN species of intruding water were not taken from the BB near‐surface data. Instead, the July 2014 intrusion was assumed to bring Scotian Shelf water with negligible ammonium and nitrite concentrations (0 μ mol kg −1 ) and nitrate concentrations (2.5 μ mol kg −1 ) and δ 15 N NO3 (4.6‰) values as observed in September 2014 in Scotian Shelf waters near Halifax (Lehmann, Buchwald, and Kienast unpubl.…”