Chloride ions, Cl-, follow actively transported Na+ ions from the nephrons into the blood. Would you not expect the Cl- concentration to decrease as fluids are extracted along the nephron?

Bicarbonate ion, HCO3- (which has a similar charge to chloride ions) also follow sodium ions into the blood. Also, potassium ions, K+ are transported into the nephron so some chloride ions and bicarbonate ions remains in the nephron to balance the charge.

Explanation:

Sodium is the primary positively charged electrolyte in extracellular fluid. Most of the solute reabsorbed in the proximal tubule is in the form of sodium bicarbonate and sodium chloride. Water is also reabsorbed in order to balance osmotic pressure

When sodium ions are reabsorbed into the blood, few of the substances that are transported with Na+ on the membrane facing the lumen of the tubules include Cl- ions, Ca2+ ions, amino acids, and glucose. Sodium is actively exchanged for K+ using ATP on the basal membrane.

In the distal convoluted tubule, K+ and H+ ions are selectively secreted into the filtrate, while Na+, Cl-, and HCO3- ions are reabsorbed to maintain pH and electrolyte balance in the blood.

Some chloride ions remains in the nephron to balance the charge of the secreted K+ ions and also due to the bicarbonate ions that are removed.

for the first question:

Ocean currents act much like a conveyer belt. they transport warm water and precipitation from the equator toward the poles and cold water from the poles back to the tropics. this, currents regulate global climate, helping to counteract the uneven distribution of solar radiation reaching Earth's surface.