A 30-year (1992-2021) time-series of Kd(PAR) at the North Sea - Baltic Sea transitional zone - trends in light attenuation and Chlorophyll a

Lars Chresten Lund-Hansen

doi:10.1016/j.rsma.2023.103367

A 30-year (1992-2021) time-series of K_d(PAR) at the North Sea - Baltic Sea transitional zone - trends in light attenuation and Chlorophyll a

Publikation: Bidrag til tidsskrift/Konferencebidrag i tidsskrift /Bidrag til avis › Tidsskriftartikel › Forskning › peer review

Abstract

Light attenuation is of fundamental importance for photosynthesis in marine and freshwater environments and quantified as K_d(PAR). A 30-year (1992–2021) long time-series of K_d(PAR) (n = 945) from Aarhus Bay, at the North Sea - Baltic Sea transition obtained with 1–5 measurements per month is analyzed. The time-series showed a weak but not statistically significant positive trend with an average K_d(PAR) of 0.30 ± 0.08 m⁻¹. Monthly based time-series of K_d(PAR) showed, in comparison, significant differences with average maximum values in March of 0.38 ± 0.09 m⁻¹ compared to a minimum in June of 0.26 ± 0.03 m⁻¹. There were statistically significant positive K_d(PAR) trends in April and December and a negative trend in October. Accordingly, the depth limit of eelgrass and macroalgae decreased from 8 to 5 m in April. The strong variability in K_d(PAR) in February and March related to the phytoplankton spring bloom in Aarhus Bay both in timing and strength, given the strong and significant correlation between Chl a and K_d(PAR). Partitioning showed that non-Chl a attenuation related to CDOM and suspended matter increased from 0.20 m⁻¹ to 0.29 m⁻¹ between 1992 and 2007 but was constant from then on. The Chl a specific attenuation coefficient varied around an average of 0.019 ± 0.008 m² (mg Chl a)⁻¹ and showed only small variations over time. The frequency of CTD casts and light measurements decreased between 1992 (n = 52 per year) and 2022 (n = 15 per year) but no parallel trends in average K_d(PAR) were observed. No significant trend (1992–2021) in annual average Chl a concentrations in Aarhus Bay was detected. The importance of high-resolution measurements in time are emphasized and at least monthly to track the strong seasonal variation.

Originalsprog	Engelsk
Artikelnummer	103367
Tidsskrift	Regional Studies in Marine Science
Vol/bind	70
ISSN	2352-4855
DOI	https://doi.org/10.1016/j.rsma.2023.103367
Status	Udgivet - feb. 2024

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title = "A 30-year (1992-2021) time-series of Kd(PAR) at the North Sea - Baltic Sea transitional zone - trends in light attenuation and Chlorophyll a",

abstract = "Light attenuation is of fundamental importance for photosynthesis in marine and freshwater environments and quantified as Kd(PAR). A 30-year (1992–2021) long time-series of Kd(PAR) (n = 945) from Aarhus Bay, at the North Sea - Baltic Sea transition obtained with 1–5 measurements per month is analyzed. The time-series showed a weak but not statistically significant positive trend with an average Kd(PAR) of 0.30 ± 0.08 m−1. Monthly based time-series of Kd(PAR) showed, in comparison, significant differences with average maximum values in March of 0.38 ± 0.09 m−1 compared to a minimum in June of 0.26 ± 0.03 m−1. There were statistically significant positive Kd(PAR) trends in April and December and a negative trend in October. Accordingly, the depth limit of eelgrass and macroalgae decreased from 8 to 5 m in April. The strong variability in Kd(PAR) in February and March related to the phytoplankton spring bloom in Aarhus Bay both in timing and strength, given the strong and significant correlation between Chl a and Kd(PAR). Partitioning showed that non-Chl a attenuation related to CDOM and suspended matter increased from 0.20 m−1 to 0.29 m−1 between 1992 and 2007 but was constant from then on. The Chl a specific attenuation coefficient varied around an average of 0.019 ± 0.008 m2 (mg Chl a)−1 and showed only small variations over time. The frequency of CTD casts and light measurements decreased between 1992 (n = 52 per year) and 2022 (n = 15 per year) but no parallel trends in average Kd(PAR) were observed. No significant trend (1992–2021) in annual average Chl a concentrations in Aarhus Bay was detected. The importance of high-resolution measurements in time are emphasized and at least monthly to track the strong seasonal variation.",

keywords = "30-year time-series, Chl a, K(PAR), North Sea - Baltic Sea transition, Trends, Variability",

author = "Lund-Hansen, {Lars Chresten}",

note = "Publisher Copyright: {\textcopyright} 2024 The Authors",

year = "2024",

month = feb,

doi = "10.1016/j.rsma.2023.103367",

language = "English",

volume = "70",

journal = "Regional Studies in Marine Science",

issn = "2352-4855",

publisher = "Elsevier",

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TY - JOUR

T1 - A 30-year (1992-2021) time-series of Kd(PAR) at the North Sea - Baltic Sea transitional zone - trends in light attenuation and Chlorophyll a

AU - Lund-Hansen, Lars Chresten

PY - 2024/2

Y1 - 2024/2

N2 - Light attenuation is of fundamental importance for photosynthesis in marine and freshwater environments and quantified as Kd(PAR). A 30-year (1992–2021) long time-series of Kd(PAR) (n = 945) from Aarhus Bay, at the North Sea - Baltic Sea transition obtained with 1–5 measurements per month is analyzed. The time-series showed a weak but not statistically significant positive trend with an average Kd(PAR) of 0.30 ± 0.08 m−1. Monthly based time-series of Kd(PAR) showed, in comparison, significant differences with average maximum values in March of 0.38 ± 0.09 m−1 compared to a minimum in June of 0.26 ± 0.03 m−1. There were statistically significant positive Kd(PAR) trends in April and December and a negative trend in October. Accordingly, the depth limit of eelgrass and macroalgae decreased from 8 to 5 m in April. The strong variability in Kd(PAR) in February and March related to the phytoplankton spring bloom in Aarhus Bay both in timing and strength, given the strong and significant correlation between Chl a and Kd(PAR). Partitioning showed that non-Chl a attenuation related to CDOM and suspended matter increased from 0.20 m−1 to 0.29 m−1 between 1992 and 2007 but was constant from then on. The Chl a specific attenuation coefficient varied around an average of 0.019 ± 0.008 m2 (mg Chl a)−1 and showed only small variations over time. The frequency of CTD casts and light measurements decreased between 1992 (n = 52 per year) and 2022 (n = 15 per year) but no parallel trends in average Kd(PAR) were observed. No significant trend (1992–2021) in annual average Chl a concentrations in Aarhus Bay was detected. The importance of high-resolution measurements in time are emphasized and at least monthly to track the strong seasonal variation.

AB - Light attenuation is of fundamental importance for photosynthesis in marine and freshwater environments and quantified as Kd(PAR). A 30-year (1992–2021) long time-series of Kd(PAR) (n = 945) from Aarhus Bay, at the North Sea - Baltic Sea transition obtained with 1–5 measurements per month is analyzed. The time-series showed a weak but not statistically significant positive trend with an average Kd(PAR) of 0.30 ± 0.08 m−1. Monthly based time-series of Kd(PAR) showed, in comparison, significant differences with average maximum values in March of 0.38 ± 0.09 m−1 compared to a minimum in June of 0.26 ± 0.03 m−1. There were statistically significant positive Kd(PAR) trends in April and December and a negative trend in October. Accordingly, the depth limit of eelgrass and macroalgae decreased from 8 to 5 m in April. The strong variability in Kd(PAR) in February and March related to the phytoplankton spring bloom in Aarhus Bay both in timing and strength, given the strong and significant correlation between Chl a and Kd(PAR). Partitioning showed that non-Chl a attenuation related to CDOM and suspended matter increased from 0.20 m−1 to 0.29 m−1 between 1992 and 2007 but was constant from then on. The Chl a specific attenuation coefficient varied around an average of 0.019 ± 0.008 m2 (mg Chl a)−1 and showed only small variations over time. The frequency of CTD casts and light measurements decreased between 1992 (n = 52 per year) and 2022 (n = 15 per year) but no parallel trends in average Kd(PAR) were observed. No significant trend (1992–2021) in annual average Chl a concentrations in Aarhus Bay was detected. The importance of high-resolution measurements in time are emphasized and at least monthly to track the strong seasonal variation.

KW - 30-year time-series

KW - Chl a

KW - K(PAR)

KW - North Sea - Baltic Sea transition

KW - Trends

KW - Variability

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U2 - 10.1016/j.rsma.2023.103367

DO - 10.1016/j.rsma.2023.103367

M3 - Journal article

AN - SCOPUS:85182237797

SN - 2352-4855

VL - 70

JO - Regional Studies in Marine Science

JF - Regional Studies in Marine Science

M1 - 103367

ER -