Quantification of new production during a winter Noctiluca scintillans bloom in the Arabian Sea

Abstract

[1] We present new data on the nitrate (new production), ammonium, urea uptake rates and f-ratios for the eastern Arabian Sea (10°to 22°N) during the late winter (northeast) monsoon, 2004, including regions of green Noctiluca scintillans bloom. A comparison of N-uptake rates of the Noctiluca dominated northern zone to the southern nonbloom zone indicates the presence of two biogeochemical regimes during the late winter monsoon: highly productive north and less productive south. The conservative estimates of photic zone-integrated total N-uptake and f-ratio are high in the north ($19 mmolNm

Constraints on global oceanic emissions of N<sub>2</sub>O from observations and models

“…Implementing this light response did not improve the model, either in combination with the O 2 and temperature responses or with the temperature response only, and was subsequently omitted. The lack of improvement in nitrification rates by adding light inhibi-tion might reflect the lower sensitivity of AOA to light found by Qin et al (2014).…”

“…We tested if including temperature, O 2 or light dependence improves the ability of the model to reproduce observed nitrification rates. Regarding the response of ammonia-oxidising Archaea (AOA), the main nitrifiers in the ocean (Francis et al, 2005;Wuchter et al, 2006;Loescher et al, 2012), to temperature, we are only aware of the measurements of Qin et al (2014). These show a ∼ 4-fold variation in maximum growth rate between three strains, which poorly constrains the temperature dependence of AOA.…”

“…N 2 O is produced either during production of NO + ρ urea )) as a function of latitude, from 15 N uptake experiments. Small dots were estimated without measuring NH + 4 or urea concentrations (Prakash et al, 2008(Prakash et al, , 2015Gandhi et al, 2010Gandhi et al, , 2012. Large dots did not give a significant linear relationship with absolute value of latitude and were therefore averaged at 0.29 ± 0.18 (Wafar et al, 2004;Varela et al, 2005Varela et al, , 2013Joubert et al, 2011;Thomalla et al, 2011;Simpson et al, 2013).…”

Revisiting the <i>Noctiluca scintillans</i> Paradox in Northern Arabian Sea

“…6). Sustained studies during the last decade have provided more information on this bloom 1,[7][8][9][10] . The northern Arabian Sea experiences strong seasonal forcing from the southwest monsoon (summer) to the northeast monsoon (winter).…”

“…Furthermore, the heterotrophic behaviour of N. scintillans sp. aided by conspicuous ammonium secretion in the vicinity, probably helps the species to outcompete the previous community, leading to large phytoplankton bloom 8 . More recently, inhibition of mixed-layer deepening during winter monsoon due to Western Indian Coastal Current has also been observed which may further restricts silicate availability 25 , leading to longer presence of N. scintillans in the water column.…”