A 2011-2018 Fukushima Perspective on North Pacific Mode Water Pathways

2021 ◽  
Author(s):  
Alison Macdonald ◽  
Sachiko Yoshida ◽  
Irina Rypina
Keyword(s):  
North Pacific ◽  
Half Life ◽  
Nuclear Power ◽  
North Pacific Ocean ◽  
Data Sets ◽  
Mode Water ◽  
Eastern Basin ◽  
Mode Waters ◽  
The North ◽  
The Pacific

<p>This investigation uses the tracer information provided by the 2011 direct ocean release of radio-isotopes, (<sup>137</sup>Cs, ~30-year half-life and <sup>134</sup>Cs, ~2-year half-life) from the Fukushima Dai-ichi nuclear power plant (FDNPP) together with hydrographic profiles to better understand the origins and pathways of mode waters in the North Pacific Ocean. While using information provided by radionuclide observations taken from across the basin, the main focus is on the eastern basin and results from analyses of two data sets 2015 (GO-SHIP) and 2018 (GEOTRACES) along the 152°W meridian. The study looks at how mode waters formed in the spring of 2011 have spread and mixed, and how they have not. Our radiocesium isotope samples tell a story of a surprisingly confined pathway for these waters and suggest that circulation to the north into the subpolar gyre occurs more quickly than circulation to the south into the subtropical gyre. They indicate that in spite of crossing 6000 km in their journey across the Pacific, the densest 2011 mode waters stayed together spreading by only a few hundred kilometers in the north/south direction, remained subsurface (below ~200 m) for most of the trip, and only saw the atmosphere again as they followed shoaling density surfaces into the boundary of the Alaska Gyre. The more recent data are sparse and do not allow direct measurement of the FDNPP specific <sup>134</sup>Cs, however they do provide some information on mode water evolution in the eastern North Pacific seven years after the accident. </p>

Weakening and Poleward Shifting of the North Pacific Subtropical Fronts from 1980 to 2018

2021 ◽  
Keyword(s):  
Mixed Layer ◽  
North Pacific ◽  
Subtropical Gyre ◽  
Hadley Cell ◽  
North Pacific Subtropical Gyre ◽  
Mode Water ◽  
Mode Waters ◽  
The North ◽  
The North Pacific ◽  
Subtropical Fronts

Abstract Recent evidence shows that the North Pacific subtropical gyre, the Kuroshio Extension (KE) and Oyashio Extension (OE) fronts have moved poleward in the past few decades. However, changes of the North Pacific Subtropical Fronts (STFs), anchored by the North Pacific subtropical countercurrent in the southern subtropical gyre, remain to be quantified. By synthesizing observations, reanalysis, and eddy-resolving ocean hindcasts, we show that the STFs, especially their eastern part, weakened (20%±5%) and moved poleward (1.6°±0.4°) from 1980 to 2018. Changes of the STFs are modified by mode waters to the north. We find that the central mode water (CMW) (180°-160°W) shows most significant weakening (18%±7%) and poleward shifting (2.4°±0.9°) trends, while the eastern part of the subtropical mode water (STMW) (160°E-180°) has similar but moderate changes (10% ± 8%; 0.9°±0.4°). Trends of the western part of the STMW (140°E-160°E) are not evident. The weakening and poleward shifting of mode waters and STFs are enhanced to the east and are mainly associated with changes of the northern deep mixed layers and outcrop lines—which have a growing northward shift as they elongate to the east. The eastern deep mixed layer shows the largest shallowing trend, where the subduction rate also decreases the most. The mixed layer and outcrop line changes are strongly coupled with the northward migration of the North Pacific subtropical gyre and the KE/OE jets as a result of the poleward expanded Hadley cell, indicating that the KE/OE fronts, mode waters, and STFs change as a whole system.

North Pacific Subtropical Mode Water Controlled by the Atlantic Multi-Decadal Variability

2020 ◽  
Author(s):  
Baolan wu ◽  
Xiaopei lin ◽  
Lisan yu
Keyword(s):  
Pacific Ocean ◽  
North Pacific ◽  
Decadal Variability ◽  
Heat Content ◽  
Northwestern Pacific ◽  
Mode Water ◽  
Subtropical Mode Water ◽  
The North ◽  
Mean Temperature ◽  
The Pacific

<p><strong>The North Pacific Subtropical Mode Water (mode water hereafter) is a vertically homogeneous thermocline water mass, occupying the entire subtropical Western Pacific Ocean. By transporting mass, heat and nutrients from the surface into the subsurface ocean, it provides memory of climate variability and is a potential source of predictability. Previous studies attributed decadal variability of the mode water mean temperature to the Pacific Decadal Oscillation (PDO). Using available observations and reanalysis data, here we show that decadal to multi-decadal variability of the mode water mean temperature is controlled by the Atlantic Multi-Decadal Variability (AMV) instead. During an AMV positive phase, warm sea surface temperatures (SSTs) in the north Atlantic Ocean weaken the subtropical North</strong> <strong>Pacific westerlies, and the anomalous easterlies in the subtropical west Pacific drive an anomalous northward Ekman transport of warm water into the mode water formation area. </strong><strong>This increases the mode water temperature through subduction</strong><strong>, driving variability of the upper-layer ocean heat content and fish catches in the Northwestern Pacific. This mechanism is supported by a long pre-industrial model simulation with multiple AMV cycles and by a Pacemaker model experiment, in which the AMV forcing alone is shown to drive the variability of the mode water. Our finding suggests that the AMV is an important driver for decadal climate and ecosystem variability and provides memory for prediction in the Pacific Ocean.</strong></p>

Biology of the Pacific Pomfret (Brama japonica) in the North Pacific Ocean

1993 ◽  
Vol 50 (12) ◽  
pp. 2608-2625 ◽  
Author(s):  
William G. Pearcy ◽  
Joseph P. Fisher ◽  
Mary M. Yoklavich
Keyword(s):  
Pacific Ocean ◽  
North Pacific ◽  
North Pacific Ocean ◽  
Gulf Of Alaska ◽  
Small Fish ◽  
Large Fish ◽  
The North ◽  
The Pacific ◽  
Subarctic Current ◽  
The North Pacific

Abundances of Pacific pomfret (Brama japonica), an epipelagic fish of the North Pacific Ocean, were estimated from gillnet catches during the summers of 1978–1989. Two size modes were common: small pomfret <1 yr old, and large fish ages 1–6. Large and small fish moved northward as temperatures increased, but large fish migrated farther north, often into the cool, low-salinity waters of the Central Subarctic Pacific. Lengths of small fish were positively correlated with latitude and negatively correlated with summer surface temperature. Interannual variations in the latitude of catches correlated with surface temperatures. Large catches were made in the eastern Gulf of Alaska (51–55°N) but modes of small pomfret were absent here, and large fish were rare at these latitudes farther to the west. Pomfret grow rapidly during their first two years of life. They are pectoral fin swimmers that swim continuously. They prey largely on gonatid squids in the region of the Subarctic Current in the Gulf of Alaska during summer. No evidence was found for aggregations on a scale ≤1 km. Differences in the incidence of tapeworm, spawning seasons, and size distributions suggest the possibility of discrete populations in the North Pacific Ocean.

Final mass balance of Fukushima released radiocaesium in our environment

2021 ◽  
Author(s):  
Michio Aoyama ◽  
Yayoi Inomata ◽  
Daisuke Tsumune ◽  
Takaki Tsubono
Keyword(s):  
Pacific Ocean ◽  
Mass Balance ◽  
North Pacific ◽  
North Pacific Ocean ◽  
Marine Biota ◽  
Mode Water ◽  
The North ◽  
Final Mass ◽  
Direct Discharge ◽  
The North Pacific

&lt;p&gt;One of the greatest results obtained by analyzing seawater samples from the North Pacific Ocean was the estimation of the total amount of 137Cs in the North Pacific to be 15-18 PBq (Aoyama et al., 2016). This estimation has been validated by two methods described by Tsubono et al. (2016) and Inomata et al. (2016). Coastal modeling results gave the amount of 137Cs direct discharge from the FDNPP to coastal waters to be (3.5 &amp;#177; 0.7) PBq (Tsumune et al., 2012) which was the first and the most accurate result. Since the amount of direct discharge was accurately determined, the amount of 137Cs released into the atmosphere was also properly determined by the mass balance consideration as discussed in Aoyama et al. (2016a).&amp;#160;&lt;/p&gt;&lt;p&gt;For the calculation of the final mass balance, we did not include several results as they did not cover the whole region, or they included the amount of atmospheric fallout as part of the direct discharge. The total amount of radiocesium released to the atmosphere was estimated to be from 8.1 PBq (Yumimoto et al., 2016) to 36 PBq (Stohl et al., 2O12). Based on mass balance consideration we conclude that (15.2-20.4) PBq of the FDNPP-derived 137Cs might be a reasonable value for the total atmospheric release (supported by Aoyama et al., 2016a; Katata et al., 2015; Mathieu et al., 2012; Saunier et al., 2013; Winiarek et al., 2014). The estimated land deposition is (3.4&amp;#8211;6.2) PBq (Aoyama et al., 2016). The estimated 137Cs inventories in the North Pacific are in the range (15.2&amp;#8211;18.3) PBq, as obtained by Tsubono et al. (2016) and&amp;#160; Inomata et al. (2016), while only (3&amp;#8211;6) PBq was the contribution from the direct discharge (consensus value, Aoyama et al., 2016), although our previous estimate was more precise, (3.5 &amp;#177; 0.7) PBq. For atmospheric deposition to the North Pacific, the estimated values are in the range (11.7&amp;#8211;14.8) PBq (Aoyama et al., 2016; Inomata et al., 2016; Tsubono et al., 2016).&lt;/p&gt;&lt;p&gt;The radiocesium inventories in the interior domains of the North Pacific Ocean have been estimated. The radiocesium inventory in the STMW (Subtropical Mode Water) is (4.2&amp;#8201;&amp;#177;&amp;#8201;1.1) PBq (Kaeriyama et al., 2016), and (7.9 &amp;#177; 1.4) PBq in the surface layer (Inomata et al., 2018b). In the CMW (Central Mode Water), the radiocesium inventory is (2.5 &amp;#177; 0.9) PBq (Inomata et al., 2018b). The radiocesium sediment inventory is (0.20 &amp;#177; 0.06) PBq (Otosaka, 2017). The inventory in marine biota might be less than 200 GBq (Aoyama et al., 2019).&lt;/p&gt;

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