contents of oxygen and nutrients in the frontal zone of the brazil and

contents of oxygen and nutrients in the frontal zone of the brazil and

Bogusław SZ PIG A N O W IC Z _______
Sea Fisheries Institute
Department of Oceanography — Gdynia
CONTENTS OF OXYGEN AND NUTRIENTS IN THE
FRONTAL ZONE OF THE BRAZIL AND FALKLAND
CURRENTS
C o n t e n t s : 1. Introduction, 2. Experim ental, 3. Results aind discussion, 4. Con­
clusions; Strcszczenie, References.
1. INTRODUCTION
Biogenic salts, i.e., inorganic salts of nitrogen, phosphorus and silicon,
a re the com pounds essential for th e p ro d u ctiv ity of a m arine ecosystem .
A dequate am ounts and ap p ro p riate m u tu a l proportions of these salts
form the basis fo r th e developm ent of life in th e sea. Intensive increase
in p rim a ry p roduction can lead to loss of balance in biogenic sa lt con­
centrations and fre q u e n tly to th e ir to tal depletion [8], The concentration
of n u trie n ts in th e photic lay er of th e ocean depends on th e in te n sity of
p rim a ry production, as w ell as the possibility of tra n sp o rt of th e salts
from deeper layers. T he euphotic lay er of th e ocean contains soluble
salts of phosphorus, n itro g en and silicon w ith in th e concentration range
of several m icrogram -atom s of th e basic elem en t p e r cubic decim eter.
P hosphorus can p a rtic ip a te in th e process of photosynthesis in th e form
of dissolved o rthophosphates or com plex ions containing m agnesium and
calcium [7], S uspended form s of phosphorus-containing organic com ­
pounds do not tak e p a rt in photosynthesis directly. Of th e nitro g en com ­
pounds, nitrates, n itrite s and am m onia salts and, to a sm all ex ten t, sim ­
p le am ino acids and u re a are biochem ically active [2, 6]. A sm all am ount
of nitro g en can be in tro d u ced to th e m arin e env iro n m en t d irectly from
th e atm osphere by som e algae (blue-green algae).
The th ird group of biogenic salts consists of dissolved silicon com po­
unds. Silicon occurs in sea w a te r m ain ly as ^ w eak orthosilicic acid
Si(OH)4 [3]. T he m a jo rity of silicon com pounds is assim ilated by th e dia-
tom s, th u s being c o n v erted fro m th e dissolved form to sp arin g ly soluble
suspensions and fu rth e r to p recip itates.
A c h aracteristic of th e region in w hich investigations w e re carried
out in M ay 1978 w as th e h ig h er co n ten ts of biogenic salts as w e ll as th e
w id er ran g e of th e ir co n cen tratio n s th a n th e d a ta p u blished in lite ra tu re
suggested. E x em p lary c o n cen tratio n d istrib u tio n of individual n u trie n ts
in sea w a te r w ith resp ect to te m p e ra tu re and sa lin ity according to
J. L. R eid e t al. [6] is show n in Fig. 1. D ata for th is diagram w e re collec­
ted in th e A rg en tin e Basin.
oxygen 02[ml/l]
phosphate PO, [yg at/l]
Fig. 1. Vertical distribution of hydrophysical and hydrochem ical elem ents at sta­
tion No. 50 (Cato Expedition, [6]).
Rys. 1. Pionow e rozm ieszczenie elem entów hydrofizycznych i hydrochem icznych na
stacji nr 50 (ekspedycja Cato, [6]).
2. EX PER IM EN T A L
T he d a ta p rese n ted below w e re collected in M ay 1978 in th e A rg en tin e
B asin (sou th w estern A tlan tic Ocean) a t th e oceanographic stations lo­
cated as show n in Fig. *2. T he follow ing w e re d eterm in ed a t each of 46
stations:
Fig. 2. Location of oceanograiphic stations.
Rys. 2. Rozm ieszczenie stacji oceanograficznych.
— dissolved oxygen c o n ten t in w a te r by th e W inkler m ethod,
— phosphates by th e M u rp h y -R iley m ethod,
— n itra te s by th e M orris-R iley m ethod, m odified by G rasshoff,
— n itrite s by th e B endschneider-R obinson m ethod,
— silicates by th e M u llin-R iley „ b lu e ” m ethod.
C alculations w ere c a rrie d out on an ELLIO T 905 com puter. S am ples
w ere collected using a BERGEN N A U TIK ty p e N ansen flask a t stan d ard
levels dow n to 2000 m, excluding th e surface lay e r dow n to 200 m. In
th e la tte r case, th e m easu rin g levels w ere d eterm in ed follow ing th e an a­
lysis of BT records.
3. RESULTS AND DISCUSSION
O x y g e n . T he cool and less saline w a te rs of th e F a lk la n d C u rre n t con­
tain ed m ore oxygen th a n th e w a rm e r and m ore saline W aters of th e
Fig. 3. Oxygen content in the surface layer. May 1978.
Rys. 3. Zawartość tlenu w w arstw ie powierzchniowej. Maj 1978,
B razil C u rre n t (Fig. 3). T he levelling effect of m eteorological conditions,
atm ospheric oxygen, insolation etc., re n d e re d th e differences in oxygen
sa tu ra tio n b etw een n o rth e rn and so u th e rn surface w a te rs insignificant
and th e fro n ta l zone in distinct. The oxygen c o n ten t w as sim ilar th ro u g h
Fig. 4. O xygen content at the 200 m level. May 1978.
Rys. 4. Zawartość tlenu na poziom ie 200 m. Maj 1978.
Fig. 5. Vertical distribution of oxygen concentration [ml 0 2/ l ] , profile 1 (45° S). May1978.
Rys. 5. P ionow y rozkład stężeń tlenu [ml 0 2/ l ] , profil 1 (45° S). Maj 1-978.
out th e w hole area and v a rie d fro m 97 to 103%. T he oxygen co n ten t
in th e surface la y e r dow n to 200 m did not change significantly. A t
a d e p th of 200 m th e ran g e of w a te rs of th e F a lk la n d and B razil
C u rre n ts as w e ll as th a t of th e fro n ta l zone w e re d istin ctly m arked
(Fig. 4). The p a tte rn of isooxygens, w ith w ell-developed g rad ie n ts a t the
junction of w a te rs from th e n o rth and south, defines th e fro n ta l zone
at this d e p th precisely. N orth of th e fro n ta l zone th e oxygen co n ten t at
100 kms
Fig. 6. Vertical distribution oxygen concentration [ml 0 2/ l ] , profile 5 (35° S). May
1978.
Rys. 6. P ionow y rozkład stężeń tlenu [ml 0 2/l] , profil 5 (35° S). Maj 1978.
th e 200 m level w as u n ifo rm and am o u n ted to ca. 5.0 m l 0 2/ l , w h ereas
th e so u th e rn p a rt contained m ore oxygen — ca. 6.75 m l 0 2/ l , a t a sa tu ra ­
tion ran g in g from 82 to 90'Vci. T he su b su rface oxygen m inim um occurred
a t th e pycnocline boundary, .below th e m ixing layer. This w as p robably
caused by increased consum ption of oxygen in th e processes of decom po­
sition of organic m a tte r (Figs. 5, 6, 7). The oxygen m axim um associa-
100 k ms
Pig. 7. V ertical distribution of oxygen concentration [ml 0 2/ l ] p rofile 6 (ica. 48° W).
May 1978.
Rys. 7. Pionow y rozkład stężeń tlenu [ml O2 /I ], profil 6 (ok. 48° W). Maj 1978.
ted w ith th e A n tarctic In te rm e d ia te W ater m ass (AAIW ) occurred to th e
n o rth of th e fro n ta l zone, a t a d e p th fro m 400 to 800 m. In th e w a te rs
of th e F a lk la n d C u rren t, i.e. in th e so u th -w est p a rt of th e reg io n inve­
stigated, th e m axim um occurred a t a d e p th of ca. 200 m. Shallow ing
of th e A n ta rc tic In te rm e d ia te W ater should be a ttrib u te d to th e u p w e lling of w a te r in a cyclonic gyre [5]. T he second (a fter th e surface) oxy­
gen m inim um occurred a t a d e p th of ca. 1200 to 1500 m and w as asso­
ciated w ith th e m ass of th e C ircum po lar W ater (CPW ) flow ing from th e
P acific p a rt of th e S o u th e rn O cean th ro u g h th e D rak e Passage. Below
th is th e oxygen c o n ten t increased by ab o u t 0.5 m l 0 2/ l [5]. T he increase
of oxygen c o n ten t observed a t 2000 m w as p ro b ab ly connected w ith
m ass of th e U pper N o rth A tlan tic Deep W ater (UNADW).
Fig. 8. Contents of nitrites and nitrates in the surface layer. May 1978.
Rys. 8. Zawartość azotynów i azotanów w w arstw ie pow ierzchniow ej. Maj 1978.
Fig. 9. Contents of phosphates and silicates in the surface layer. May 1978.
Rys. 9. Zawartość fosforanów i krzem ianów w w arstw ie powierzchniowej. Maj 1978.
100 kms
i---------- 1
Fig. 10. Vertical distribution of nitrates concentrations t^gat/1], profile 1 (45° S).
May 1978.
Rys. 10. Klonowe rozm ieszczenie stężeń azotanów [jj.gat/1], profil 1 (45° S). Maj 1978.
12 — Oceanologia Nr 14
100 kms
Fig. 11. V ertical distribution of nitrates concentrations [ugat N N O 3 / I ] , profile 5
(35° S). May 1978.
Rys. 11. P ionow e rozm ieszczenie st^zen azotan6w [[xgat N N O 3 / I ] , profil 5 (35° S).
Maj 1978.
N i t r o g e n . T he co n ten ts of n itro g en -co n tain in g salts in th e surface
lay e r v a rie d over a v e ry w ide range, from alm ost com plete depletion to
n e a rly 11 [xgat N / 1 in th e case of n itra te s (Fig. 8a) and fro m zero to
alm ost 0.4 ^.igat N / l in th e case of n itrite s (Fig. 8b). In v e rtica l d istri­
bution, th e co n ten ts of n itra te s in creased 'with d e p th to 30 (igat N / l in
th e n o rth e rn p a rt of th e a re a in v estig ated and to 35 [igat N / l in th e
s o u th -e a st (Figs. 10, 11). T he co n ten ts of n itrite s in th e active la y e r of
th e ocean w as of th e o rd er of te n th s of ¡xgat/1 dow n to th e pycnocline,
and decreased to zero below th e d ensity jum p in th e m a jo rity of cases.
P h o s p h o r u s . The su rface lay e r contained p h osphorus com pounds in
co n cen tratio n s ran g in g fro m below th e detection lim it to 1.0 jigat P / 1,
th e o ccurrence of th e h ig h est co n cen tratio n s coinciding ro u g h ly w ith
those of n itra te s (Fig. 9a). The co n ten ts of p h osphates increased s te a ­
dily w ith depth, reach in g co n cen tratio n s of th e order of 2.5 to 2.75
Ugat P /1 in th e 1500— 2000 m la y e r (Figs. 12, 13, 14).
100 kms
Fig. 12. Verticail distribution of phosphates concentrations tugat/'l], profile 1 (45° S).
May 1978.
Rys. 12. Pionowe rozm ieszczenie stężeń fosforanów [[¿gat/l], profil 1 (45° S). Maj 1978.
*
100 kms
Fig. 13. Vertical distribution
(35® S ). M ay 1978>
Rys. 13. Pionowe
Maj 1978.
of phosphates concentrations
rozm ieszczenie stężeń fosforanów
[ngat P /1 ], profile 5
[ngat P / l ] ,
profil 5 (35° S).
100 kms
Fig. 14. Vertical distribution of phosphates concentrations [jigat/1], profile 6 (ca.
48» W). May 1978.
Rys. 14. Pionowe rozm ieszczenie stężeń fosforanów [a g a t/l], profil 6 (ok. 48° W).
Maj 1978.
S i l i c o n . T he c o n cen tratio n d istrib u tio n of silicates in th e surface la ­
y e r d iffered som ew hat from th a t of phosphates and n itra te s. T he values
of h ig h er concentrations in te rm ix ed w ith low er ones from an irre g u la r
p a tte rn ran g in g from 0.49 to 3.89 ^igat S i/1 (Fig. 9B). In v e rtic a l d istri­
bution, silicates ex h ib ited a high degree of stratificatio n , in creasin g ste a ­
d ily w ith d e p th and reach in g th e con cen tratio n s of th e o rd er of 50 figat
S i/1 in th e n o rth and 70 jigat S i7! in th e so u th -w e st (Figs. 15, 16, 17).
100 knns
Fig.
M ay
Rys.
Maj
15. V ertical distribution of silicates concentrations [^gat/1], profile 1 (45° S).
1978.
15. P ionow e rozm ieszczenie stężeń krzem ianów, [¡xgat/1], profil 1 (45° S).
1978.
Fig.
May
Rys.
Maj
16. Vertical distribution of silicates concentrations [u,gat Si / l ] , profile 5 (35° S).
1978.
16. Pionowe rozm ieszczenie stężeń krzem ianów [¡xgat S i/l] , profil 5 (35° S).
1978.
\
100 kms
Fig.
May
Rys.
Maj
17. V ertical distribution of silicates concentrations [^gat/1], profile 6 (ca. 48° W).
1978.
17. Pinnow e rozm ieszczenie stężeń krzem ianów [[ig a t/l], profil 6 (ok. 48° W).
1978.
4. CONCLUSIONS
The surface lay e r bounded from below b y a sh arp pycnocline w as di­
s tin c tly deficient in biogenic salts, and Was also th e re th a t a q u asi-g ra­
d ien t of con cen tratio n of all biogenic salts w as form ed. This w as re la te d
to im peded v e rtic a l m ixing th ro u g h th e pycnocline and hence to r e d u ­
ced tra n s p o rt of salts from th e deeper lay e rs of th e ocean. A t th e points
w h e re th e pycnocline w as diffused, th e co n cen tratio n s of n u trie n ts in crea­
sed ste a d ily w ith d ep th dow n to th e m ea su rem e n t lim it (2000 m) w ith th e
exception of n itrite s, th e p resen ce of w h ich w as occasionally observed
below th e pycnocline.
T he regions of m axim um c o n cen tratio n s of phosphates and n itra te s
coincided w ith those of th e occurrence of cyclonic gyres b rin g in g fe rtile
deep w a te rs to th e surface in th e fro n ta l zone [5].
W eighted average co n ten ts of biogenic salts (¡xgat/1):
E lem ent B razil
C u rre n t
F a lk la n d
C u rre n t
F ro n ta l zone L a y e r (m):
Si
1.0 — 1.5
1.0 — 1.8
2.4 — 3.6
3.9 — 4.9
1.2 — 1.7
1.1 — 3.5
0— 50
0— 100
p
0.27— 0.33
0.27— 0.42
1.08— 1.45
1.29— 1.45
0.57— 0.58
0.58— 0.75
0— 50
0— 100
N -N O 3
1.1 — 1.6
2.6 — 2.8
5.5 — 8.8
6.6 — 9.3
2.9 — 7.8
2.9 — 10.8
0— 50
0— 100
T he analysis of th e e x p e rim e n tal d a ta confirm s th e conclusion th a t
th e w a te rs c arried by th e F a lk la n d C u rre n t a re considerably ric h e r in
n u trie n ts th a n those of th e B razil C u rre n t, w h e re as th e fro n ta l zone
co n stitu tes th e region of in te rm e d ia te concentrations.
B ogusław S Z P IGANOW ICZ
Morski Instytut Rybacki
Zakład Oceanografii w Gdyni
ZAWARTOŚĆ TLENU I SUBSTANCJI BIOGENICZNYCH W STRE­
FIE FRONTALNEJ PRĄDÓW BRAZYLIJSKIEGO I FALKLANDZKIEGO
Streszczenie
Opracowanie zawiera krótki opis dystrybucji soli biogenicznych w zachodniej części
Basenu A rgentyńskiego do głębokości 2000 m z podkreśleniem obszaru m ieszania
wód Prądu Brazylijskiego i Falklandzikiego.
Obserwowana ostra piknoklina utrudniała m ieszanie pionow e wód, stąd w ar­
stwa powierzchniowa była w yraźnie uboższa w sole biogeniczne. M iejsca w ystąpie­
nia ostrej piknokliny charakteryzow ały się w yraźnym i gradientam i stężeń, nato­
m iast tam, gdzie .piknoklina była rozmyta, stężenia biog&iów w zrastały system a­
tycznie aż do granicy pomiaru, tj. 2000 m, z w yjątkiem azotynów, których obecność
pod piknokliną stwierdzona była sporadycznie. Obszary najw yższych stężeń fosfo­
ranów i azotanów pokrywają się z m iejscam i w ystąpienia cyklonalnych w irów
wynoszących żyzne w ody głębinow e w strefie frontalnej prądów.
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